Pacemaker Explained

Configuring Pacemaker Clusters

Abstract

This document definitively explains Pacemaker’s features and capabilities, particularly the XML syntax used in Pacemaker’s Cluster Information Base (CIB).

Table of Contents

1. Introduction

1.1. The Scope of this Document

This document is intended to be an exhaustive reference for configuring Pacemaker. To achieve this, it focuses on the XML syntax used to configure the CIB.

For those that are allergic to XML, multiple higher-level front-ends (both command-line and GUI) are available. These tools will not be covered in this document, though the concepts explained here should make the functionality of these tools more easily understood.

Users may be interested in other parts of the Pacemaker documentation set, such as Clusters from Scratch, a step-by-step guide to setting up an example cluster, and Pacemaker Administration, a guide to maintaining a cluster.

1.2. What Is Pacemaker?

Pacemaker is a high-availability cluster resource manager – software that runs on a set of hosts (a cluster of nodes) in order to preserve integrity and minimize downtime of desired services (resources). [1] It is maintained by the ClusterLabs community.

Pacemaker’s key features include:

  • Detection of and recovery from node- and service-level failures
  • Ability to ensure data integrity by fencing faulty nodes
  • Support for one or more nodes per cluster
  • Support for multiple resource interface standards (anything that can be scripted can be clustered)
  • Support (but no requirement) for shared storage
  • Support for practically any redundancy configuration (active/passive, N+1, etc.)
  • Automatically replicated configuration that can be updated from any node
  • Ability to specify cluster-wide relationships between services, such as ordering, colocation and anti-colocation
  • Support for advanced service types, such as clones (services that need to be active on multiple nodes), promotable clones (clones that can run in one of two roles), and containerized services
  • Unified, scriptable cluster management tools

Note

Fencing

Fencing, also known as STONITH (an acronym for Shoot The Other Node In The Head), is the ability to ensure that it is not possible for a node to be running a service. This is accomplished via fence devices such as intelligent power switches that cut power to the target, or intelligent network switches that cut the target’s access to the local network.

Pacemaker represents fence devices as a special class of resource.

A cluster cannot safely recover from certain failure conditions, such as an unresponsive node, without fencing.

1.2.1. Cluster Architecture

At a high level, a cluster can be viewed as having these parts (which together are often referred to as the cluster stack):

  • Resources: These are the reason for the cluster’s being – the services that need to be kept highly available.
  • Resource agents: These are scripts or operating system components that start, stop, and monitor resources, given a set of resource parameters. These provide a uniform interface between Pacemaker and the managed services.
  • Fence agents: These are scripts that execute node fencing actions, given a target and fence device parameters.
  • Cluster membership layer: This component provides reliable messaging, membership, and quorum information about the cluster. Currently, Pacemaker supports Corosync as this layer.
  • Cluster resource manager: Pacemaker provides the brain that processes and reacts to events that occur in the cluster. These events may include nodes joining or leaving the cluster; resource events caused by failures, maintenance, or scheduled activities; and other administrative actions. To achieve the desired availability, Pacemaker may start and stop resources and fence nodes.
  • Cluster tools: These provide an interface for users to interact with the cluster. Various command-line and graphical (GUI) interfaces are available.

Most managed services are not, themselves, cluster-aware. However, many popular open-source cluster filesystems make use of a common Distributed Lock Manager (DLM), which makes direct use of Corosync for its messaging and membership capabilities and Pacemaker for the ability to fence nodes.

Example cluster stack
1.2.2. Pacemaker Architecture

Pacemaker itself is composed of multiple daemons that work together:

  • pacemakerd
  • pacemaker-attrd
  • pacemaker-based
  • pacemaker-controld
  • pacemaker-execd
  • pacemaker-fenced
  • pacemaker-schedulerd
Pacemaker software components

Pacemaker’s main process (pacemakerd) spawns all the other daemons, and respawns them if they unexpectedly exit.

The Cluster Information Base (CIB) is an XML representation of the cluster’s configuration and the state of all nodes and resources. The CIB manager (pacemaker-based) keeps the CIB synchronized across the cluster, and handles requests to modify it.

The attribute manager (pacemaker-attrd) maintains a database of attributes for all nodes, keeps it synchronized across the cluster, and handles requests to modify them. These attributes are usually recorded in the CIB.

Given a snapshot of the CIB as input, the scheduler (pacemaker-schedulerd) determines what actions are necessary to achieve the desired state of the cluster.

The local executor (pacemaker-execd) handles requests to execute resource agents on the local cluster node, and returns the result.

The fencer (pacemaker-fenced) handles requests to fence nodes. Given a target node, the fencer decides which cluster node(s) should execute which fencing device(s), and calls the necessary fencing agents (either directly, or via requests to the fencer peers on other nodes), and returns the result.

The controller (pacemaker-controld) is Pacemaker’s coordinator, maintaining a consistent view of the cluster membership and orchestrating all the other components.

Pacemaker centralizes cluster decision-making by electing one of the controller instances as the Designated Controller (DC). Should the elected DC process (or the node it is on) fail, a new one is quickly established. The DC responds to cluster events by taking a current snapshot of the CIB, feeding it to the scheduler, then asking the executors (either directly on the local node, or via requests to controller peers on other nodes) and the fencer to execute any necessary actions.

Note

Old daemon names

The Pacemaker daemons were renamed in version 2.0. You may still find references to the old names, especially in documentation targeted to version 1.1.

Old name New name
attrd pacemaker-attrd
cib pacemaker-based
crmd pacemaker-controld
lrmd pacemaker-execd
stonithd pacemaker-fenced
pacemaker_remoted pacemaker-remoted
1.2.3. Node Redundancy Designs

Pacemaker supports practically any node redundancy configuration including Active/Active, Active/Passive, N+1, N+M, N-to-1 and N-to-N.

Active/passive clusters with two (or more) nodes using Pacemaker and DRBD are a cost-effective high-availability solution for many situations. One of the nodes provides the desired services, and if it fails, the other node takes over.

Active/Passive Redundancy

Pacemaker also supports multiple nodes in a shared-failover design, reducing hardware costs by allowing several active/passive clusters to be combined and share a common backup node.

Shared Failover

When shared storage is available, every node can potentially be used for failover. Pacemaker can even run multiple copies of services to spread out the workload. This is sometimes called N to N Redundancy.

N to N Redundancy

Footnotes

[1]Cluster is sometimes used in other contexts to refer to hosts grouped together for other purposes, such as high-performance computing (HPC), but Pacemaker is not intended for those purposes.

2. Cluster-Wide Configuration

2.1. Configuration Layout

The cluster is defined by the Cluster Information Base (CIB), which uses XML notation. The simplest CIB, an empty one, looks like this:

An empty configuration

<cib crm_feature_set="3.6.0" validate-with="pacemaker-3.5" epoch="1" num_updates="0" admin_epoch="0">
  <configuration>
    <crm_config/>
    <nodes/>
    <resources/>
    <constraints/>
  </configuration>
  <status/>
</cib>

The empty configuration above contains the major sections that make up a CIB:

  • cib: The entire CIB is enclosed with a cib element. Certain fundamental settings are defined as attributes of this element.
    • configuration: This section – the primary focus of this document – contains traditional configuration information such as what resources the cluster serves and the relationships among them.
      • crm_config: cluster-wide configuration options
      • nodes: the machines that host the cluster
      • resources: the services run by the cluster
      • constraints: indications of how resources should be placed
    • status: This section contains the history of each resource on each node. Based on this data, the cluster can construct the complete current state of the cluster. The authoritative source for this section is the local executor (pacemaker-execd process) on each cluster node, and the cluster will occasionally repopulate the entire section. For this reason, it is never written to disk, and administrators are advised against modifying it in any way.

In this document, configuration settings will be described as properties or options based on how they are defined in the CIB:

  • Properties are XML attributes of an XML element.
  • Options are name-value pairs expressed as nvpair child elements of an XML element.

Normally, you will use command-line tools that abstract the XML, so the distinction will be unimportant; both properties and options are cluster settings you can tweak.

2.2. CIB Properties

Certain settings are defined by CIB properties (that is, attributes of the cib tag) rather than with the rest of the cluster configuration in the configuration section.

The reason is simply a matter of parsing. These options are used by the configuration database which is, by design, mostly ignorant of the content it holds. So the decision was made to place them in an easy-to-find location.

CIB Properties
Attribute Description
admin_epoch

When a node joins the cluster, the cluster performs a check to see which node has the best configuration. It asks the node with the highest (admin_epoch, epoch, num_updates) tuple to replace the configuration on all the nodes – which makes setting them, and setting them correctly, very important. admin_epoch is never modified by the cluster; you can use this to make the configurations on any inactive nodes obsolete.

Warning: Never set this value to zero. In such cases, the cluster cannot tell the difference between your configuration and the “empty” one used when nothing is found on disk.

epoch

The cluster increments this every time the configuration is updated (usually by the administrator).

num_updates

The cluster increments this every time the configuration or status is updated (usually by the cluster) and resets it to 0 when epoch changes.

validate-with

Determines the type of XML validation that will be done on the configuration. If set to none, the cluster will not verify that updates conform to the DTD (nor reject ones that don’t).

cib-last-written

Indicates when the configuration was last written to disk. Maintained by the cluster; for informational purposes only.

have-quorum

Indicates if the cluster has quorum. If false, this may mean that the cluster cannot start resources or fence other nodes (see no-quorum-policy below). Maintained by the cluster.

dc-uuid

Indicates which cluster node is the current leader. Used by the cluster when placing resources and determining the order of some events. Maintained by the cluster.

2.3. Cluster Options

Cluster options, as you might expect, control how the cluster behaves when confronted with various situations.

They are grouped into sets within the crm_config section. In advanced configurations, there may be more than one set. (This will be described later in the chapter on Rules where we will show how to have the cluster use different sets of options during working hours than during weekends.) For now, we will describe the simple case where each option is present at most once.

You can obtain an up-to-date list of cluster options, including their default values, by running the man pacemaker-schedulerd and man pacemaker-controld commands.

Cluster Options
Option Default Description
cluster-name  

An (optional) name for the cluster as a whole. This is mostly for users’ convenience for use as desired in administration, but this can be used in the Pacemaker configuration in Rules (as the #cluster-name node attribute. It may also be used by higher-level tools when displaying cluster information, and by certain resource agents (for example, the ocf:heartbeat:GFS2 agent stores the cluster name in filesystem meta-data).

dc-version  

Version of Pacemaker on the cluster’s DC. Determined automatically by the cluster. Often includes the hash which identifies the exact Git changeset it was built from. Used for diagnostic purposes.

cluster-infrastructure  

The messaging stack on which Pacemaker is currently running. Determined automatically by the cluster. Used for informational and diagnostic purposes.

no-quorum-policy stop

What to do when the cluster does not have quorum. Allowed values:

  • ignore: continue all resource management
  • freeze: continue resource management, but don’t recover resources from nodes not in the affected partition
  • stop: stop all resources in the affected cluster partition
  • demote: demote promotable resources and stop all other resources in the affected cluster partition (since 2.0.5)
  • suicide: fence all nodes in the affected cluster partition
batch-limit 0

The maximum number of actions that the cluster may execute in parallel across all nodes. The “correct” value will depend on the speed and load of your network and cluster nodes. If zero, the cluster will impose a dynamically calculated limit only when any node has high load. If -1, the cluster will not impose any limit.

migration-limit -1

The number of live migration actions that the cluster is allowed to execute in parallel on a node. A value of -1 means unlimited.

symmetric-cluster true

Whether resources can run on any node by default (if false, a resource is allowed to run on a node only if a location constraint enables it)

stop-all-resources false

Whether all resources should be disallowed from running (can be useful during maintenance)

stop-orphan-resources true

Whether resources that have been deleted from the configuration should be stopped. This value takes precedence over is-managed (that is, even unmanaged resources will be stopped when orphaned if this value is true

stop-orphan-actions true

Whether recurring operations that have been deleted from the configuration should be cancelled

start-failure-is-fatal true

Whether a failure to start a resource on a particular node prevents further start attempts on that node? If false, the cluster will decide whether the node is still eligible based on the resource’s current failure count and migration-threshold.

enable-startup-probes true

Whether the cluster should check the pre-existing state of resources when the cluster starts

maintenance-mode false

Whether the cluster should refrain from monitoring, starting and stopping resources

stonith-enabled true

Whether the cluster is allowed to fence nodes (for example, failed nodes and nodes with resources that can’t be stopped.

If true, at least one fence device must be configured before resources are allowed to run.

If false, unresponsive nodes are immediately assumed to be running no resources, and resource recovery on online nodes starts without any further protection (which can mean data loss if the unresponsive node still accesses shared storage, for example). See also the requires resource meta-attribute.

stonith-action reboot

Action the cluster should send to the fence agent when a node must be fenced. Allowed values are reboot, off, and (for legacy agents only) poweroff.

stonith-timeout 60s

How long to wait for on, off, and reboot fence actions to complete by default.

stonith-max-attempts 10

How many times fencing can fail for a target before the cluster will no longer immediately re-attempt it.

stonith-watchdog-timeout 0

If nonzero, and the cluster detects have-watchdog as true, then watchdog-based self-fencing will be performed via SBD when fencing is required, without requiring a fencing resource explicitly configured.

If this is set to a positive value, unseen nodes are assumed to self-fence within this much time.

Warning: It must be ensured that this value is larger than the SBD_WATCHDOG_TIMEOUT environment variable on all nodes. Pacemaker verifies the settings individually on all nodes and prevents startup or shuts down if configured wrongly on the fly. It is strongly recommended that SBD_WATCHDOG_TIMEOUT be set to the same value on all nodes.

If this is set to a negative value, and SBD_WATCHDOG_TIMEOUT is set, twice that value will be used.

Warning: In this case, it is essential (and currently not verified by pacemaker) that SBD_WATCHDOG_TIMEOUT is set to the same value on all nodes.

concurrent-fencing false

Whether the cluster is allowed to initiate multiple fence actions concurrently. Fence actions initiated externally, such as via the stonith_admin tool or an application such as DLM, or by the fencer itself such as recurring device monitors and status and list commands, are not limited by this option.

fence-reaction stop

How should a cluster node react if notified of its own fencing? A cluster node may receive notification of its own fencing if fencing is misconfigured, or if fabric fencing is in use that doesn’t cut cluster communication. Allowed values are stop to attempt to immediately stop pacemaker and stay stopped, or panic to attempt to immediately reboot the local node, falling back to stop on failure. The default is likely to be changed to panic in a future release. (since 2.0.3)

priority-fencing-delay 0

Apply this delay to any fencing targeting the lost nodes with the highest total resource priority in case we don’t have the majority of the nodes in our cluster partition, so that the more significant nodes potentially win any fencing match (especially meaningful in a split-brain of a 2-node cluster). A promoted resource instance takes the resource’s priority plus 1 if the resource’s priority is not 0. Any static or random delays introduced by pcmk_delay_base and pcmk_delay_max configured for the corresponding fencing resources will be added to this delay. This delay should be significantly greater than (safely twice) the maximum delay from those parameters. (since 2.0.4)

cluster-delay 60s

Estimated maximum round-trip delay over the network (excluding action execution). If the DC requires an action to be executed on another node, it will consider the action failed if it does not get a response from the other node in this time (after considering the action’s own timeout). The “correct” value will depend on the speed and load of your network and cluster nodes.

dc-deadtime 20s

How long to wait for a response from other nodes during startup. The “correct” value will depend on the speed/load of your network and the type of switches used.

cluster-ipc-limit 500

The maximum IPC message backlog before one cluster daemon will disconnect another. This is of use in large clusters, for which a good value is the number of resources in the cluster multiplied by the number of nodes. The default of 500 is also the minimum. Raise this if you see “Evicting client” messages for cluster daemon PIDs in the logs.

pe-error-series-max -1

The number of scheduler inputs resulting in errors to save. Used when reporting problems. A value of -1 means unlimited (report all), and 0 means none.

pe-warn-series-max 5000

The number of scheduler inputs resulting in warnings to save. Used when reporting problems. A value of -1 means unlimited (report all), and 0 means none.

pe-input-series-max 4000

The number of “normal” scheduler inputs to save. Used when reporting problems. A value of -1 means unlimited (report all), and 0 means none.

enable-acl false

Whether Access Control Lists (ACLs) should be used to authorize modifications to the CIB

placement-strategy default

How the cluster should allocate resources to nodes (see Utilization and Placement Strategy). Allowed values are default, utilization, balanced, and minimal.

node-health-strategy none

How the cluster should react to node health attributes (see Tracking Node Health). Allowed values are none, migrate-on-red, only-green, progressive, and custom.

node-health-base 0

The base health score assigned to a node. Only used when node-health-strategy is progressive.

node-health-green 0

The score to use for a node health attribute whose value is green. Only used when node-health-strategy is progressive or custom.

node-health-yellow 0

The score to use for a node health attribute whose value is yellow. Only used when node-health-strategy is progressive or custom.

node-health-red 0

The score to use for a node health attribute whose value is red. Only used when node-health-strategy is progressive or custom.

cluster-recheck-interval 15min

Pacemaker is primarily event-driven, and looks ahead to know when to recheck the cluster for failure timeouts and most time-based rules (since 2.0.3). However, it will also recheck the cluster after this amount of inactivity. This has two goals: rules with date_spec are only guaranteed to be checked this often, and it also serves as a fail-safe for some kinds of scheduler bugs. A value of 0 disables this polling; positive values are a time interval.

shutdown-lock false

The default of false allows active resources to be recovered elsewhere when their node is cleanly shut down, which is what the vast majority of users will want. However, some users prefer to make resources highly available only for failures, with no recovery for clean shutdowns. If this option is true, resources active on a node when it is cleanly shut down are kept “locked” to that node (not allowed to run elsewhere) until they start again on that node after it rejoins (or for at most shutdown-lock-limit, if set). Stonith resources and Pacemaker Remote connections are never locked. Clone and bundle instances and the promoted role of promotable clones are currently never locked, though support could be added in a future release. Locks may be manually cleared using the --refresh option of crm_resource (both the resource and node must be specified; this works with remote nodes if their connection resource’s target-role is set to Stopped, but not if Pacemaker Remote is stopped on the remote node without disabling the connection resource). (since 2.0.4)

shutdown-lock-limit 0

If shutdown-lock is true, and this is set to a nonzero time duration, locked resources will be allowed to start after this much time has passed since the node shutdown was initiated, even if the node has not rejoined. (This works with remote nodes only if their connection resource’s target-role is set to Stopped.) (since 2.0.4)

remove-after-stop false

Deprecated Should the cluster remove resources from Pacemaker’s executor after they are stopped? Values other than the default are, at best, poorly tested and potentially dangerous. This option is deprecated and will be removed in a future release.

startup-fencing true

Advanced Use Only: Should the cluster fence unseen nodes at start-up? Setting this to false is unsafe, because the unseen nodes could be active and running resources but unreachable.

election-timeout 2min

Advanced Use Only: If you need to adjust this value, it probably indicates the presence of a bug.

shutdown-escalation 20min

Advanced Use Only: If you need to adjust this value, it probably indicates the presence of a bug.

join-integration-timeout 3min

Advanced Use Only: If you need to adjust this value, it probably indicates the presence of a bug.

join-finalization-timeout 30min

Advanced Use Only: If you need to adjust this value, it probably indicates the presence of a bug.

transition-delay 0s

Advanced Use Only: Delay cluster recovery for the configured interval to allow for additional or related events to occur. This can be useful if your configuration is sensitive to the order in which ping updates arrive. Enabling this option will slow down cluster recovery under all conditions.

3. Cluster Nodes

3.1. Defining a Cluster Node

Each cluster node will have an entry in the nodes section containing at least an ID and a name. A cluster node’s ID is defined by the cluster layer (Corosync).

Example Corosync cluster node entry

<node id="101" uname="pcmk-1"/>

In normal circumstances, the admin should let the cluster populate this information automatically from the cluster layer.

3.1.1. Where Pacemaker Gets the Node Name

The name that Pacemaker uses for a node in the configuration does not have to be the same as its local hostname. Pacemaker uses the following for a Corosync node’s name, in order of most preferred first:

  • The value of name in the nodelist section of corosync.conf
  • The value of ring0_addr in the nodelist section of corosync.conf
  • The local hostname (value of uname -n)

If the cluster is running, the crm_node -n command will display the local node’s name as used by the cluster.

If a Corosync nodelist is used, crm_node --name-for-id with a Corosync node ID will display the name used by the node with the given Corosync nodeid, for example:

crm_node --name-for-id 2

3.2. Node Attributes

Pacemaker allows node-specific values to be specified using node attributes. A node attribute has a name, and may have a distinct value for each node.

Node attributes come in two types, permanent and transient. Permanent node attributes are kept within the node entry, and keep their values even if the cluster restarts on a node. Transient node attributes are kept in the CIB’s status section, and go away when the cluster stops on the node.

While certain node attributes have specific meanings to the cluster, they are mainly intended to allow administrators and resource agents to track any information desired.

For example, an administrator might choose to define node attributes for how much RAM and disk space each node has, which OS each uses, or which server room rack each node is in.

Users can configure Rules that use node attributes to affect where resources are placed.

3.2.1. Setting and querying node attributes

Node attributes can be set and queried using the crm_attribute and attrd_updater commands, so that the user does not have to deal with XML configuration directly.

Here is an example command to set a permanent node attribute, and the XML configuration that would be generated:

Result of using crm_attribute to specify which kernel pcmk-1 is running

# crm_attribute --type nodes --node pcmk-1 --name kernel --update $(uname -r)
<node id="1" uname="pcmk-1">
   <instance_attributes id="nodes-1-attributes">
     <nvpair id="nodes-1-kernel" name="kernel" value="3.10.0-862.14.4.el7.x86_64"/>
   </instance_attributes>
</node>

To read back the value that was just set:

# crm_attribute --type nodes --node pcmk-1 --name kernel --query
scope=nodes  name=kernel value=3.10.0-862.14.4.el7.x86_64

The --type nodes indicates that this is a permanent node attribute; --type status would indicate a transient node attribute.

3.2.2. Special node attributes

Certain node attributes have special meaning to the cluster.

Node attribute names beginning with # are considered reserved for these special attributes. Some special attributes do not start with #, for historical reasons.

Certain special attributes are set automatically by the cluster, should never be modified directly, and can be used only within Rules; these are listed under built-in node attributes.

For true/false values, the cluster considers a value of “1”, “y”, “yes”, “on”, or “true” (case-insensitively) to be true, “0”, “n”, “no”, “off”, “false”, or unset to be false, and anything else to be an error.

Node attributes with special significance
Name Description
fail-count-*

Attributes whose names start with fail-count- are managed by the cluster to track how many times particular resource operations have failed on this node. These should be queried and cleared via the crm_failcount or crm_resource --cleanup commands rather than directly.

last-failure-*

Attributes whose names start with last-failure- are managed by the cluster to track when particular resource operations have most recently failed on this node. These should be cleared via the crm_failcount or crm_resource --cleanup commands rather than directly.

maintenance

Similar to the maintenance-mode cluster option, but for a single node. If true, resources will not be started or stopped on the node, resources and individual clone instances running on the node will become unmanaged, and any recurring operations for those will be cancelled.

Warning: Restarting pacemaker on a node that is in single-node maintenance mode will likely lead to undesirable effects. If maintenance is set as a transient attribute, it will be erased when Pacemaker is stopped, which will immediately take the node out of maintenance mode and likely get it fenced. Even if permanent, if Pacemaker is restarted, any resources active on the node will have their local history erased when the node rejoins, so the cluster will no longer consider them running on the node and thus will consider them managed again, leading them to be started elsewhere. This behavior might be improved in a future release.

probe_complete

This is managed by the cluster to detect when nodes need to be reprobed, and should never be used directly.

resource-discovery-enabled

If the node is a remote node, fencing is enabled, and this attribute is explicitly set to false (unset means true in this case), resource discovery (probes) will not be done on this node. This is highly discouraged; the resource-discovery location constraint property is preferred for this purpose.

shutdown

This is managed by the cluster to orchestrate the shutdown of a node, and should never be used directly.

site-name

If set, this will be used as the value of the #site-name node attribute used in rules. (If not set, the value of the cluster-name cluster option will be used as #site-name instead.)

standby

If true, the node is in standby mode. This is typically set and queried via the crm_standby command rather than directly.

terminate

If the value is true or begins with any nonzero number, the node will be fenced. This is typically set by tools rather than directly.

#digests-*

Attributes whose names start with #digests- are managed by the cluster to detect when Unfencing needs to be redone, and should never be used directly.

#node-unfenced

When the node was last unfenced (as seconds since the epoch). This is managed by the cluster and should never be used directly.

4. Cluster Resources

4.1. What is a Cluster Resource?

A resource is a service made highly available by a cluster. The simplest type of resource, a primitive resource, is described in this chapter. More complex forms, such as groups and clones, are described in later chapters.

Every primitive resource has a resource agent. A resource agent is an external program that abstracts the service it provides and present a consistent view to the cluster.

This allows the cluster to be agnostic about the resources it manages. The cluster doesn’t need to understand how the resource works because it relies on the resource agent to do the right thing when given a start, stop or monitor command. For this reason, it is crucial that resource agents are well-tested.

Typically, resource agents come in the form of shell scripts. However, they can be written using any technology (such as C, Python or Perl) that the author is comfortable with.

4.2. Resource Classes

Pacemaker supports several classes of agents:

  • OCF
  • LSB
  • Systemd
  • Upstart (deprecated)
  • Service
  • Fencing
  • Nagios Plugins
4.2.1. Open Cluster Framework

The OCF standard [1] is basically an extension of the Linux Standard Base conventions for init scripts to:

  • support parameters,
  • make them self-describing, and
  • make them extensible

OCF specs have strict definitions of the exit codes that actions must return [2].

The cluster follows these specifications exactly, and giving the wrong exit code will cause the cluster to behave in ways you will likely find puzzling and annoying. In particular, the cluster needs to distinguish a completely stopped resource from one which is in some erroneous and indeterminate state.

Parameters are passed to the resource agent as environment variables, with the special prefix OCF_RESKEY_. So, a parameter which the user thinks of as ip will be passed to the resource agent as OCF_RESKEY_ip. The number and purpose of the parameters is left to the resource agent; however, the resource agent should use the meta-data command to advertise any that it supports.

The OCF class is the most preferred as it is an industry standard, highly flexible (allowing parameters to be passed to agents in a non-positional manner) and self-describing.

For more information, see the reference and the Resource Agents chapter of Pacemaker Administration.

4.2.2. Linux Standard Base

LSB resource agents are more commonly known as init scripts. If a full path is not given, they are assumed to be located in /etc/init.d.

Commonly, they are provided by the OS distribution. In order to be used with a Pacemaker cluster, they must conform to the LSB specification [3].

Warning

Many distributions or particular software packages claim LSB compliance but ship with broken init scripts. For details on how to check whether your init script is LSB-compatible, see the Resource Agents chapter of Pacemaker Administration. Common problematic violations of the LSB standard include:

  • Not implementing the status operation at all
  • Not observing the correct exit status codes for start/stop/status actions
  • Starting a started resource returns an error
  • Stopping a stopped resource returns an error

Important

Remember to make sure the computer is not configured to start any services at boot time – that should be controlled by the cluster.

4.2.3. Systemd

Most Linux distributions have replaced the old SysV style of initialization daemons and scripts with Systemd.

Pacemaker is able to manage these services if they are present.

Instead of init scripts, systemd has unit files. Generally, the services (unit files) are provided by the OS distribution, but there are online guides for converting from init scripts [4].

Important

Remember to make sure the computer is not configured to start any services at boot time – that should be controlled by the cluster.

4.2.4. Upstart

Some distributions replaced the old SysV style of initialization daemons (and scripts) with Upstart.

Pacemaker is able to manage these services if they are present.

Instead of init scripts, Upstart has jobs. Generally, the services (jobs) are provided by the OS distribution.

Important

Remember to make sure the computer is not configured to start any services at boot time – that should be controlled by the cluster.

Warning

Upstart support is deprecated in Pacemaker. Upstart is no longer an actively maintained project, and test platforms for it are no longer readily usable. Support will likely be dropped entirely at the next major release of Pacemaker.

4.2.5. System Services

Since there are various types of system services (systemd, upstart, and lsb), Pacemaker supports a special service alias which intelligently figures out which one applies to a given cluster node.

This is particularly useful when the cluster contains a mix of systemd, upstart, and lsb.

In order, Pacemaker will try to find the named service as:

  • an LSB init script
  • a Systemd unit file
  • an Upstart job
4.2.6. STONITH

The STONITH class is used exclusively for fencing-related resources. This is discussed later in Fencing.

4.2.7. Nagios Plugins

Nagios Plugins [5] are a way to monitor services. Pacemaker can use these as resources, to react to a change in the service’s status.

To use plugins as resources, Pacemaker must have been built with support, and OCF-style meta-data for the plugins must be installed on nodes that can run them. Meta-data for several common plugins is provided by the nagios-agents-metadata project.

The supported parameters for such a resource are same as the long options of the plugin.

Start and monitor actions for plugin resources are implemented as invoking the plugin. A plugin result of “OK” (0) is treated as success, a result of “WARN” (1) is treated as a successful but degraded service, and any other result is considered a failure.

A plugin resource is not going to change its status after recovery by restarting the plugin, so using them alone does not make sense with on-fail set (or left to default) to restart. Another value could make sense, for example, if you want to fence or standby nodes that cannot reach some external service.

A more common use case for plugin resources is to configure them with a container meta-attribute set to the name of another resource that actually makes the service available, such as a virtual machine or container.

With container set, the plugin resource will automatically be colocated with the containing resource and ordered after it, and the containing resource will be considered failed if the plugin resource fails. This allows monitoring of a service inside a virtual machine or container, with recovery of the virtual machine or container if the service fails.

Configuring a virtual machine as a guest node, or a container as a bundle, is the preferred way of monitoring a service inside, but plugin resources can be useful when it is not practical to modify the virtual machine or container image for this purpose.

4.3. Resource Properties

These values tell the cluster which resource agent to use for the resource, where to find that resource agent and what standards it conforms to.

Properties of a Primitive Resource
Field Description
id

Your name for the resource

class

The standard the resource agent conforms to. Allowed values: lsb, nagios, ocf, service, stonith, systemd, upstart

type

The name of the Resource Agent you wish to use. E.g. IPaddr or Filesystem

provider

The OCF spec allows multiple vendors to supply the same resource agent. To use the OCF resource agents supplied by the Heartbeat project, you would specify heartbeat here.

The XML definition of a resource can be queried with the crm_resource tool. For example:

# crm_resource --resource Email --query-xml

might produce:

A system resource definition

<primitive id="Email" class="service" type="exim"/>

Note

One of the main drawbacks to system services (LSB, systemd or Upstart) resources is that they do not allow any parameters!

An OCF resource definition

<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
   <instance_attributes id="Public-IP-params">
      <nvpair id="Public-IP-ip" name="ip" value="192.0.2.2"/>
   </instance_attributes>
</primitive>

4.4. Resource Options

Resources have two types of options: meta-attributes and instance attributes. Meta-attributes apply to any type of resource, while instance attributes are specific to each resource agent.

4.4.1. Resource Meta-Attributes

Meta-attributes are used by the cluster to decide how a resource should behave and can be easily set using the --meta option of the crm_resource command.

Meta-attributes of a Primitive Resource
Field Default Description
priority 0

If not all resources can be active, the cluster will stop lower priority resources in order to keep higher priority ones active.

critical true

Use this value as the default for influence in all colocation constraints involving this resource, as well as the implicit colocation constraints created if this resource is in a group. For details, see Colocation Influence. (since 2.1.0)

target-role Started

What state should the cluster attempt to keep this resource in? Allowed values:

  • Stopped: Force the resource to be stopped
  • Started: Allow the resource to be started (and in the case of promotable clone resources, promoted if appropriate)
  • Unpromoted: Allow the resource to be started, but only in the unpromoted role if the resource is promotable
  • Promoted: Equivalent to Started
is-managed TRUE

Is the cluster allowed to start and stop the resource? Allowed values: true, false

maintenance FALSE

Similar to the maintenance-mode cluster option, but for a single resource. If true, the resource will not be started, stopped, or monitored on any node. This differs from is-managed in that monitors will not be run. Allowed values: true, false

resource-stickiness 1 for individual clone instances, 0 for all other resources

A score that will be added to the current node when a resource is already active. This allows running resources to stay where they are, even if they would be placed elsewhere if they were being started from a stopped state.

requires quorum for resources with a class of stonith, otherwise unfencing if unfencing is active in the cluster, otherwise fencing if stonith-enabled is true, otherwise quorum

Conditions under which the resource can be started. Allowed values:

  • nothing: can always be started
  • quorum: The cluster can only start this resource if a majority of the configured nodes are active
  • fencing: The cluster can only start this resource if a majority of the configured nodes are active and any failed or unknown nodes have been fenced
  • unfencing: The cluster can only start this resource if a majority of the configured nodes are active and any failed or unknown nodes have been fenced and only on nodes that have been unfenced
migration-threshold INFINITY

How many failures may occur for this resource on a node, before this node is marked ineligible to host this resource. A value of 0 indicates that this feature is disabled (the node will never be marked ineligible); by constrast, the cluster treats INFINITY (the default) as a very large but finite number. This option has an effect only if the failed operation specifies on-fail as restart (the default), and additionally for failed start operations, if the cluster property start-failure-is-fatal is false.

failure-timeout 0

How many seconds to wait before acting as if the failure had not occurred, and potentially allowing the resource back to the node on which it failed. A value of 0 indicates that this feature is disabled.

multiple-active stop_start

What should the cluster do if it ever finds the resource active on more than one node? Allowed values:

  • block: mark the resource as unmanaged
  • stop_only: stop all active instances and leave them that way
  • stop_start: stop all active instances and start the resource in one location only
allow-migrate TRUE for ocf:pacemaker:remote resources, FALSE otherwise Whether the cluster should try to “live migrate” this resource when it needs to be moved (see Migrating Resources)
container-attribute-target   Specific to bundle resources; see Bundle Node Attributes
remote-node   The name of the Pacemaker Remote guest node this resource is associated with, if any. If specified, this both enables the resource as a guest node and defines the unique name used to identify the guest node. The guest must be configured to run the Pacemaker Remote daemon when it is started. WARNING: This value cannot overlap with any resource or node IDs.
remote-port 3121 If remote-node is specified, the port on the guest used for its Pacemaker Remote connection. The Pacemaker Remote daemon on the guest must be configured to listen on this port.
remote-addr value of remote-node If remote-node is specified, the IP address or hostname used to connect to the guest via Pacemaker Remote. The Pacemaker Remote daemon on the guest must be configured to accept connections on this address.
remote-connect-timeout 60s If remote-node is specified, how long before a pending guest connection will time out.

As an example of setting resource options, if you performed the following commands on an LSB Email resource:

# crm_resource --meta --resource Email --set-parameter priority --parameter-value 100
# crm_resource -m -r Email -p multiple-active -v block

the resulting resource definition might be:

An LSB resource with cluster options

<primitive id="Email" class="lsb" type="exim">
  <meta_attributes id="Email-meta_attributes">
    <nvpair id="Email-meta_attributes-priority" name="priority" value="100"/>
    <nvpair id="Email-meta_attributes-multiple-active" name="multiple-active" value="block"/>
  </meta_attributes>
</primitive>

In addition to the cluster-defined meta-attributes described above, you may also configure arbitrary meta-attributes of your own choosing. Most commonly, this would be done for use in rules. For example, an IT department might define a custom meta-attribute to indicate which company department each resource is intended for. To reduce the chance of name collisions with cluster-defined meta-attributes added in the future, it is recommended to use a unique, organization-specific prefix for such attributes.

4.4.2. Setting Global Defaults for Resource Meta-Attributes

To set a default value for a resource option, add it to the rsc_defaults section with crm_attribute. For example,

# crm_attribute --type rsc_defaults --name is-managed --update false

would prevent the cluster from starting or stopping any of the resources in the configuration (unless of course the individual resources were specifically enabled by having their is-managed set to true).

4.4.3. Resource Instance Attributes

The resource agents of some resource classes (lsb, systemd and upstart not among them) can be given parameters which determine how they behave and which instance of a service they control.

If your resource agent supports parameters, you can add them with the crm_resource command. For example,

# crm_resource --resource Public-IP --set-parameter ip --parameter-value 192.0.2.2

would create an entry in the resource like this:

An example OCF resource with instance attributes

<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
   <instance_attributes id="params-public-ip">
      <nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
   </instance_attributes>
</primitive>

For an OCF resource, the result would be an environment variable called OCF_RESKEY_ip with a value of 192.0.2.2.

The list of instance attributes supported by an OCF resource agent can be found by calling the resource agent with the meta-data command. The output contains an XML description of all the supported attributes, their purpose and default values.

Displaying the metadata for the Dummy resource agent template

# export OCF_ROOT=/usr/lib/ocf
# $OCF_ROOT/resource.d/pacemaker/Dummy meta-data
<?xml version="1.0"?>
<!DOCTYPE resource-agent SYSTEM "ra-api-1.dtd">
<resource-agent name="Dummy" version="2.0">
<version>1.1</version>

<longdesc lang="en">
This is a dummy OCF resource agent. It does absolutely nothing except keep track
of whether it is running or not, and can be configured so that actions fail or
take a long time. Its purpose is primarily for testing, and to serve as a
template for resource agent writers.
</longdesc>
<shortdesc lang="en">Example stateless resource agent</shortdesc>

<parameters>
<parameter name="state" unique-group="state">
<longdesc lang="en">
Location to store the resource state in.
</longdesc>
<shortdesc lang="en">State file</shortdesc>
<content type="string" default="/var/run/Dummy-RESOURCE_ID.state" />
</parameter>

<parameter name="passwd" reloadable="1">
<longdesc lang="en">
Fake password field
</longdesc>
<shortdesc lang="en">Password</shortdesc>
<content type="string" default="" />
</parameter>

<parameter name="fake" reloadable="1">
<longdesc lang="en">
Fake attribute that can be changed to cause a reload
</longdesc>
<shortdesc lang="en">Fake attribute that can be changed to cause a reload</shortdesc>
<content type="string" default="dummy" />
</parameter>

<parameter name="op_sleep" reloadable="1">
<longdesc lang="en">
Number of seconds to sleep during operations.  This can be used to test how
the cluster reacts to operation timeouts.
</longdesc>
<shortdesc lang="en">Operation sleep duration in seconds.</shortdesc>
<content type="string" default="0" />
</parameter>

<parameter name="fail_start_on" reloadable="1">
<longdesc lang="en">
Start, migrate_from, and reload-agent actions will return failure if running on
the host specified here, but the resource will run successfully anyway (future
monitor calls will find it running). This can be used to test on-fail=ignore.
</longdesc>
<shortdesc lang="en">Report bogus start failure on specified host</shortdesc>
<content type="string" default="" />
</parameter>
<parameter name="envfile" reloadable="1">
<longdesc lang="en">
If this is set, the environment will be dumped to this file for every call.
</longdesc>
<shortdesc lang="en">Environment dump file</shortdesc>
<content type="string" default="" />
</parameter>

</parameters>

<actions>
<action name="start"        timeout="20s" />
<action name="stop"         timeout="20s" />
<action name="monitor"      timeout="20s" interval="10s" depth="0"/>
<action name="reload"       timeout="20s" />
<action name="reload-agent" timeout="20s" />
<action name="migrate_to"   timeout="20s" />
<action name="migrate_from" timeout="20s" />
<action name="validate-all" timeout="20s" />
<action name="meta-data"    timeout="5s" />
</actions>
</resource-agent>

4.5. Resource Operations

Operations are actions the cluster can perform on a resource by calling the resource agent. Resource agents must support certain common operations such as start, stop, and monitor, and may implement any others.

Operations may be explicitly configured for two purposes: to override defaults for options (such as timeout) that the cluster will use whenever it initiates the operation, and to run an operation on a recurring basis (for example, to monitor the resource for failure).

An OCF resource with a non-default start timeout

<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
  <operations>
     <op id="Public-IP-start" name="start" timeout="60s"/>
  </operations>
  <instance_attributes id="params-public-ip">
     <nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
  </instance_attributes>
</primitive>

Pacemaker identifies operations by a combination of name and interval, so this combination must be unique for each resource. That is, you should not configure two operations for the same resource with the same name and interval.

4.5.1. Operation Properties

Operation properties may be specified directly in the op element as XML attributes, or in a separate meta_attributes block as nvpair elements. XML attributes take precedence over nvpair elements if both are specified.

Properties of an Operation
Field Default Description
id  

A unique name for the operation.

name  

The action to perform. This can be any action supported by the agent; common values include monitor, start, and stop.

interval 0

How frequently (in seconds) to perform the operation. A value of 0 means “when needed”. A positive value defines a recurring action, which is typically used with monitor.

timeout  

How long to wait before declaring the action has failed

on-fail

Varies by action:

  • stop: fence if stonith-enabled is true or block otherwise
  • demote: on-fail of the monitor action with role set to Promoted, if present, enabled, and configured to a value other than demote, or restart otherwise
  • all other actions: restart

The action to take if this action ever fails. Allowed values:

  • ignore: Pretend the resource did not fail.
  • block: Don’t perform any further operations on the resource.
  • stop: Stop the resource and do not start it elsewhere.
  • demote: Demote the resource, without a full restart. This is valid only for promote actions, and for monitor actions with both a nonzero interval and role set to Promoted; for any other action, a configuration error will be logged, and the default behavior will be used. (since 2.0.5)
  • restart: Stop the resource and start it again (possibly on a different node).
  • fence: STONITH the node on which the resource failed.
  • standby: Move all resources away from the node on which the resource failed.
enabled TRUE

If false, ignore this operation definition. This is typically used to pause a particular recurring monitor operation; for instance, it can complement the respective resource being unmanaged (is-managed=false), as this alone will not block any configured monitoring. Disabling the operation does not suppress all actions of the given type. Allowed values: true, false.

record-pending TRUE

If true, the intention to perform the operation is recorded so that GUIs and CLI tools can indicate that an operation is in progress. This is best set as an operation default (see Setting Global Defaults for Operations). Allowed values: true, false.

role  

Run the operation only on node(s) that the cluster thinks should be in the specified role. This only makes sense for recurring monitor operations. Allowed (case-sensitive) values: Stopped, Started, and in the case of promotable clone resources, Unpromoted and Promoted.

Note

When on-fail is set to demote, recovery from failure by a successful demote causes the cluster to recalculate whether and where a new instance should be promoted. The node with the failure is eligible, so if promotion scores have not changed, it will be promoted again.

There is no direct equivalent of migration-threshold for the promoted role, but the same effect can be achieved with a location constraint using a rule with a node attribute expression for the resource’s fail count.

For example, to immediately ban the promoted role from a node with any failed promote or promoted instance monitor:

<rsc_location id="loc1" rsc="my_primitive">
    <rule id="rule1" score="-INFINITY" role="Promoted" boolean-op="or">
      <expression id="expr1" attribute="fail-count-my_primitive#promote_0"
        operation="gte" value="1"/>
      <expression id="expr2" attribute="fail-count-my_primitive#monitor_10000"
        operation="gte" value="1"/>
    </rule>
</rsc_location>

This example assumes that there is a promotable clone of the my_primitive resource (note that the primitive name, not the clone name, is used in the rule), and that there is a recurring 10-second-interval monitor configured for the promoted role (fail count attributes specify the interval in milliseconds).

4.5.2. Monitoring Resources for Failure

When Pacemaker first starts a resource, it runs one-time monitor operations (referred to as probes) to ensure the resource is running where it’s supposed to be, and not running where it’s not supposed to be. (This behavior can be affected by the resource-discovery location constraint property.)

Other than those initial probes, Pacemaker will not (by default) check that the resource continues to stay healthy [6]. You must configure monitor operations explicitly to perform these checks.

An OCF resource with a recurring health check

<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
  <operations>
     <op id="Public-IP-start" name="start" timeout="60s"/>
     <op id="Public-IP-monitor" name="monitor" interval="60s"/>
  </operations>
  <instance_attributes id="params-public-ip">
     <nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
  </instance_attributes>
</primitive>

By default, a monitor operation will ensure that the resource is running where it is supposed to. The target-role property can be used for further checking.

For example, if a resource has one monitor operation with interval=10 role=Started and a second monitor operation with interval=11 role=Stopped, the cluster will run the first monitor on any nodes it thinks should be running the resource, and the second monitor on any nodes that it thinks should not be running the resource (for the truly paranoid, who want to know when an administrator manually starts a service by mistake).

Note

Currently, monitors with role=Stopped are not implemented for clone resources.

4.5.3. Monitoring Resources When Administration is Disabled

Recurring monitor operations behave differently under various administrative settings:

  • When a resource is unmanaged (by setting is-managed=false): No monitors will be stopped.

    If the unmanaged resource is stopped on a node where the cluster thinks it should be running, the cluster will detect and report that it is not, but it will not consider the monitor failed, and will not try to start the resource until it is managed again.

    Starting the unmanaged resource on a different node is strongly discouraged and will at least cause the cluster to consider the resource failed, and may require the resource’s target-role to be set to Stopped then Started to be recovered.

  • When a node is put into standby: All resources will be moved away from the node, and all monitor operations will be stopped on the node, except those specifying role as Stopped (which will be newly initiated if appropriate).

  • When the cluster is put into maintenance mode: All resources will be marked as unmanaged. All monitor operations will be stopped, except those specifying role as Stopped (which will be newly initiated if appropriate). As with single unmanaged resources, starting a resource on a node other than where the cluster expects it to be will cause problems.

4.5.4. Setting Global Defaults for Operations

You can change the global default values for operation properties in a given cluster. These are defined in an op_defaults section of the CIB’s configuration section, and can be set with crm_attribute. For example,

# crm_attribute --type op_defaults --name timeout --update 20s

would default each operation’s timeout to 20 seconds. If an operation’s definition also includes a value for timeout, then that value would be used for that operation instead.

4.5.5. When Implicit Operations Take a Long Time

The cluster will always perform a number of implicit operations: start, stop and a non-recurring monitor operation used at startup to check whether the resource is already active. If one of these is taking too long, then you can create an entry for them and specify a longer timeout.

An OCF resource with custom timeouts for its implicit actions

<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
  <operations>
     <op id="public-ip-startup" name="monitor" interval="0" timeout="90s"/>
     <op id="public-ip-start" name="start" interval="0" timeout="180s"/>
     <op id="public-ip-stop" name="stop" interval="0" timeout="15min"/>
  </operations>
  <instance_attributes id="params-public-ip">
     <nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
  </instance_attributes>
</primitive>
4.5.6. Multiple Monitor Operations

Provided no two operations (for a single resource) have the same name and interval, you can have as many monitor operations as you like. In this way, you can do a superficial health check every minute and progressively more intense ones at higher intervals.

To tell the resource agent what kind of check to perform, you need to provide each monitor with a different value for a common parameter. The OCF standard creates a special parameter called OCF_CHECK_LEVEL for this purpose and dictates that it is “made available to the resource agent without the normal OCF_RESKEY prefix”.

Whatever name you choose, you can specify it by adding an instance_attributes block to the op tag. It is up to each resource agent to look for the parameter and decide how to use it.

An OCF resource with two recurring health checks, performing different levels of checks specified via OCF_CHECK_LEVEL.

<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
   <operations>
      <op id="public-ip-health-60" name="monitor" interval="60">
         <instance_attributes id="params-public-ip-depth-60">
            <nvpair id="public-ip-depth-60" name="OCF_CHECK_LEVEL" value="10"/>
         </instance_attributes>
      </op>
      <op id="public-ip-health-300" name="monitor" interval="300">
         <instance_attributes id="params-public-ip-depth-300">
            <nvpair id="public-ip-depth-300" name="OCF_CHECK_LEVEL" value="20"/>
         </instance_attributes>
     </op>
   </operations>
   <instance_attributes id="params-public-ip">
       <nvpair id="public-ip-level" name="ip" value="192.0.2.2"/>
   </instance_attributes>
</primitive>
4.5.7. Disabling a Monitor Operation

The easiest way to stop a recurring monitor is to just delete it. However, there can be times when you only want to disable it temporarily. In such cases, simply add enabled=false to the operation’s definition.

Example of an OCF resource with a disabled health check

<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
   <operations>
      <op id="public-ip-check" name="monitor" interval="60s" enabled="false"/>
   </operations>
   <instance_attributes id="params-public-ip">
      <nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
   </instance_attributes>
</primitive>

This can be achieved from the command line by executing:

# cibadmin --modify --xml-text '<op id="public-ip-check" enabled="false"/>'

Once you’ve done whatever you needed to do, you can then re-enable it with

# cibadmin --modify --xml-text '<op id="public-ip-check" enabled="true"/>'
[1]See https://github.com/ClusterLabs/OCF-spec/tree/master/ra. The Pacemaker implementation has been somewhat extended from the OCF specs.
[2]The resource-agents source code includes the ocf-tester script, which can be useful in this regard.
[3]See http://refspecs.linux-foundation.org/LSB_3.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html for the LSB Spec as it relates to init scripts.
[4]For example, http://0pointer.de/blog/projects/systemd-for-admins-3.html
[5]The project has two independent forks, hosted at https://www.nagios-plugins.org/ and https://www.monitoring-plugins.org/. Output from both projects’ plugins is similar, so plugins from either project can be used with pacemaker.
[6]Currently, anyway. Automatic monitoring operations may be added in a future version of Pacemaker.

5. Resource Constraints

5.1. Scores

Scores of all kinds are integral to how the cluster works. Practically everything from moving a resource to deciding which resource to stop in a degraded cluster is achieved by manipulating scores in some way.

Scores are calculated per resource and node. Any node with a negative score for a resource can’t run that resource. The cluster places a resource on the node with the highest score for it.

5.1.1. Infinity Math

Pacemaker implements INFINITY (or equivalently, +INFINITY) internally as a score of 1,000,000. Addition and subtraction with it follow these three basic rules:

  • Any value + INFINITY = INFINITY
  • Any value - INFINITY = -INFINITY
  • INFINITY - INFINITY = -INFINITY

Note

What if you want to use a score higher than 1,000,000? Typically this possibility arises when someone wants to base the score on some external metric that might go above 1,000,000.

The short answer is you can’t.

The long answer is it is sometimes possible work around this limitation creatively. You may be able to set the score to some computed value based on the external metric rather than use the metric directly. For nodes, you can store the metric as a node attribute, and query the attribute when computing the score (possibly as part of a custom resource agent).

5.2. Deciding Which Nodes a Resource Can Run On

Location constraints tell the cluster which nodes a resource can run on.

There are two alternative strategies. One way is to say that, by default, resources can run anywhere, and then the location constraints specify nodes that are not allowed (an opt-out cluster). The other way is to start with nothing able to run anywhere, and use location constraints to selectively enable allowed nodes (an opt-in cluster).

Whether you should choose opt-in or opt-out depends on your personal preference and the make-up of your cluster. If most of your resources can run on most of the nodes, then an opt-out arrangement is likely to result in a simpler configuration. On the other-hand, if most resources can only run on a small subset of nodes, an opt-in configuration might be simpler.

5.2.1. Location Properties
Attributes of a rsc_location Element
Attribute Default Description
id  

A unique name for the constraint (required)

rsc  

The name of the resource to which this constraint applies. A location constraint must either have a rsc, have a rsc-pattern, or contain at least one resource set.

rsc-pattern  

A pattern matching the names of resources to which this constraint applies. The syntax is the same as POSIX extended regular expressions, with the addition of an initial ! indicating that resources not matching the pattern are selected. If the regular expression contains submatches, and the constraint is governed by a rule, the submatches can be referenced as %1 through %9 in the rule’s score-attribute or a rule expression’s attribute. A location constraint must either have a rsc, have a rsc-pattern, or contain at least one resource set.

node  

The name of the node to which this constraint applies. A location constraint must either have a node and score, or contain at least one rule.

score  

Positive values indicate a preference for running the affected resource(s) on node – the higher the value, the stronger the preference. Negative values indicate the resource(s) should avoid this node (a value of -INFINITY changes “should” to “must”). A location constraint must either have a node and score, or contain at least one rule.

resource-discovery always

Whether Pacemaker should perform resource discovery (that is, check whether the resource is already running) for this resource on this node. This should normally be left as the default, so that rogue instances of a service can be stopped when they are running where they are not supposed to be. However, there are two situations where disabling resource discovery is a good idea: when a service is not installed on a node, discovery might return an error (properly written OCF agents will not, so this is usually only seen with other agent types); and when Pacemaker Remote is used to scale a cluster to hundreds of nodes, limiting resource discovery to allowed nodes can significantly boost performance.

  • always: Always perform resource discovery for the specified resource on this node.
  • never: Never perform resource discovery for the specified resource on this node. This option should generally be used with a -INFINITY score, although that is not strictly required.
  • exclusive: Perform resource discovery for the specified resource only on this node (and other nodes similarly marked as exclusive). Multiple location constraints using exclusive discovery for the same resource across different nodes creates a subset of nodes resource-discovery is exclusive to. If a resource is marked for exclusive discovery on one or more nodes, that resource is only allowed to be placed within that subset of nodes.

Warning

Setting resource-discovery to never or exclusive removes Pacemaker’s ability to detect and stop unwanted instances of a service running where it’s not supposed to be. It is up to the system administrator (you!) to make sure that the service can never be active on nodes without resource-discovery (such as by leaving the relevant software uninstalled).

5.2.2. Asymmetrical “Opt-In” Clusters

To create an opt-in cluster, start by preventing resources from running anywhere by default:

# crm_attribute --name symmetric-cluster --update false

Then start enabling nodes. The following fragment says that the web server prefers sles-1, the database prefers sles-2 and both can fail over to sles-3 if their most preferred node fails.

Opt-in location constraints for two resources

<constraints>
    <rsc_location id="loc-1" rsc="Webserver" node="sles-1" score="200"/>
    <rsc_location id="loc-2" rsc="Webserver" node="sles-3" score="0"/>
    <rsc_location id="loc-3" rsc="Database" node="sles-2" score="200"/>
    <rsc_location id="loc-4" rsc="Database" node="sles-3" score="0"/>
</constraints>
5.2.3. Symmetrical “Opt-Out” Clusters

To create an opt-out cluster, start by allowing resources to run anywhere by default:

# crm_attribute --name symmetric-cluster --update true

Then start disabling nodes. The following fragment is the equivalent of the above opt-in configuration.

Opt-out location constraints for two resources

<constraints>
    <rsc_location id="loc-1" rsc="Webserver" node="sles-1" score="200"/>
    <rsc_location id="loc-2-do-not-run" rsc="Webserver" node="sles-2" score="-INFINITY"/>
    <rsc_location id="loc-3-do-not-run" rsc="Database" node="sles-1" score="-INFINITY"/>
    <rsc_location id="loc-4" rsc="Database" node="sles-2" score="200"/>
</constraints>
5.2.4. What if Two Nodes Have the Same Score

If two nodes have the same score, then the cluster will choose one. This choice may seem random and may not be what was intended, however the cluster was not given enough information to know any better.

Constraints where a resource prefers two nodes equally

<constraints>
    <rsc_location id="loc-1" rsc="Webserver" node="sles-1" score="INFINITY"/>
    <rsc_location id="loc-2" rsc="Webserver" node="sles-2" score="INFINITY"/>
    <rsc_location id="loc-3" rsc="Database" node="sles-1" score="500"/>
    <rsc_location id="loc-4" rsc="Database" node="sles-2" score="300"/>
    <rsc_location id="loc-5" rsc="Database" node="sles-2" score="200"/>
</constraints>

In the example above, assuming no other constraints and an inactive cluster, Webserver would probably be placed on sles-1 and Database on sles-2. It would likely have placed Webserver based on the node’s uname and Database based on the desire to spread the resource load evenly across the cluster. However other factors can also be involved in more complex configurations.

5.3. Specifying the Order in which Resources Should Start/Stop

Ordering constraints tell the cluster the order in which certain resource actions should occur.

Important

Ordering constraints affect only the ordering of resource actions; they do not require that the resources be placed on the same node. If you want resources to be started on the same node and in a specific order, you need both an ordering constraint and a colocation constraint (see Placing Resources Relative to other Resources), or alternatively, a group (see Groups - A Syntactic Shortcut).

5.3.1. Ordering Properties
Attributes of a rsc_order Element
Field Default Description
id  

A unique name for the constraint

first  

Name of the resource that the then resource depends on

then  

Name of the dependent resource

first-action start

The action that the first resource must complete before then-action can be initiated for the then resource. Allowed values: start, stop, promote, demote.

then-action value of first-action

The action that the then resource can execute only after the first-action on the first resource has completed. Allowed values: start, stop, promote, demote.

kind Mandatory

How to enforce the constraint. Allowed values:

  • Mandatory: then-action will never be initiated for the then resource unless and until first-action successfully completes for the first resource.
  • Optional: The constraint applies only if both specified resource actions are scheduled in the same transition (that is, in response to the same cluster state). This means that then-action is allowed on the then resource regardless of the state of the first resource, but if both actions happen to be scheduled at the same time, they will be ordered.
  • Serialize: Ensure that the specified actions are never performed concurrently for the specified resources. First-action and then-action can be executed in either order, but one must complete before the other can be initiated. An example use case is when resource start-up puts a high load on the host.
symmetrical TRUE for Mandatory and Optional kinds. FALSE for Serialize kind.

If true, the reverse of the constraint applies for the opposite action (for example, if B starts after A starts, then B stops before A stops). Serialize orders cannot be symmetrical.

Promote and demote apply to promotable clone resources.

5.3.2. Optional and mandatory ordering

Here is an example of ordering constraints where Database must start before Webserver, and IP should start before Webserver if they both need to be started:

Optional and mandatory ordering constraints

<constraints>
    <rsc_order id="order-1" first="IP" then="Webserver" kind="Optional"/>
    <rsc_order id="order-2" first="Database" then="Webserver" kind="Mandatory" />
</constraints>

Because the above example lets symmetrical default to TRUE, Webserver must be stopped before Database can be stopped, and Webserver should be stopped before IP if they both need to be stopped.

5.4. Placing Resources Relative to other Resources

Colocation constraints tell the cluster that the location of one resource depends on the location of another one.

Colocation has an important side-effect: it affects the order in which resources are assigned to a node. Think about it: You can’t place A relative to B unless you know where B is [1].

So when you are creating colocation constraints, it is important to consider whether you should colocate A with B, or B with A.

Important

Colocation constraints affect only the placement of resources; they do not require that the resources be started in a particular order. If you want resources to be started on the same node and in a specific order, you need both an ordering constraint (see Specifying the Order in which Resources Should Start/Stop) and a colocation constraint, or alternatively, a group (see Groups - A Syntactic Shortcut).

5.4.1. Colocation Properties
Attributes of a rsc_colocation Constraint
Field Default Description
id  

A unique name for the constraint (required).

rsc  

The name of a resource that should be located relative to with-rsc. A colocation constraint must either contain at least one resource set, or specify both rsc and with-rsc.

with-rsc  

The name of the resource used as the colocation target. The cluster will decide where to put this resource first and then decide where to put rsc. A colocation constraint must either contain at least one resource set, or specify both rsc and with-rsc.

node-attribute #uname

If rsc and with-rsc are specified, this node attribute must be the same on the node running rsc and the node running with-rsc for the constraint to be satisfied. (For details, see Colocation by Node Attribute.)

score 0

Positive values indicate the resources should run on the same node. Negative values indicate the resources should run on different nodes. Values of +/- INFINITY change “should” to “must”.

rsc-role Started

If rsc and with-rsc are specified, and rsc is a promotable clone, the constraint applies only to rsc instances in this role. Allowed values: Started, Promoted, Unpromoted. For details, see Promotable Clone Constraints.

with-rsc-role Started

If rsc and with-rsc are specified, and with-rsc is a promotable clone, the constraint applies only to with-rsc instances in this role. Allowed values: Started, Promoted, Unpromoted. For details, see Promotable Clone Constraints.

influence value of critical meta-attribute for rsc

Whether to consider the location preferences of rsc when with-rsc is already active. Allowed values: true, false. For details, see Colocation Influence. (since 2.1.0)

5.4.2. Mandatory Placement

Mandatory placement occurs when the constraint’s score is +INFINITY or -INFINITY. In such cases, if the constraint can’t be satisfied, then the rsc resource is not permitted to run. For score=INFINITY, this includes cases where the with-rsc resource is not active.

If you need resource A to always run on the same machine as resource B, you would add the following constraint:

Mandatory colocation constraint for two resources

<rsc_colocation id="colocate" rsc="A" with-rsc="B" score="INFINITY"/>

Remember, because INFINITY was used, if B can’t run on any of the cluster nodes (for whatever reason) then A will not be allowed to run. Whether A is running or not has no effect on B.

Alternatively, you may want the opposite – that A cannot run on the same machine as B. In this case, use score="-INFINITY".

Mandatory anti-colocation constraint for two resources

<rsc_colocation id="anti-colocate" rsc="A" with-rsc="B" score="-INFINITY"/>

Again, by specifying -INFINITY, the constraint is binding. So if the only place left to run is where B already is, then A may not run anywhere.

As with INFINITY, B can run even if A is stopped. However, in this case A also can run if B is stopped, because it still meets the constraint of A and B not running on the same node.

5.4.3. Advisory Placement

If mandatory placement is about “must” and “must not”, then advisory placement is the “I’d prefer if” alternative. For constraints with scores greater than -INFINITY and less than INFINITY, the cluster will try to accommodate your wishes but may ignore them if the alternative is to stop some of the cluster resources.

As in life, where if enough people prefer something it effectively becomes mandatory, advisory colocation constraints can combine with other elements of the configuration to behave as if they were mandatory.

Advisory colocation constraint for two resources

<rsc_colocation id="colocate-maybe" rsc="A" with-rsc="B" score="500"/>
5.4.4. Colocation by Node Attribute

The node-attribute property of a colocation constraints allows you to express the requirement, “these resources must be on similar nodes”.

As an example, imagine that you have two Storage Area Networks (SANs) that are not controlled by the cluster, and each node is connected to one or the other. You may have two resources r1 and r2 such that r2 needs to use the same SAN as r1, but doesn’t necessarily have to be on the same exact node. In such a case, you could define a node attribute named san, with the value san1 or san2 on each node as appropriate. Then, you could colocate r2 with r1 using node-attribute set to san.

5.4.5. Colocation Influence

By default, if A is colocated with B, the cluster will take into account A’s preferences when deciding where to place B, to maximize the chance that both resources can run.

For a detailed look at exactly how this occurs, see Colocation Explained.

However, if influence is set to false in the colocation constraint, this will happen only if B is inactive and needing to be started. If B is already active, A’s preferences will have no effect on placing B.

An example of what effect this would have and when it would be desirable would be a nonessential reporting tool colocated with a resource-intensive service that takes a long time to start. If the reporting tool fails enough times to reach its migration threshold, by default the cluster will want to move both resources to another node if possible. Setting influence to false on the colocation constraint would mean that the reporting tool would be stopped in this situation instead, to avoid forcing the service to move.

The critical resource meta-attribute is a convenient way to specify the default for all colocation constraints and groups involving a particular resource.

Note

If a noncritical resource is a member of a group, all later members of the group will be treated as noncritical, even if they are marked as (or left to default to) critical.

5.5. Resource Sets

Resource sets allow multiple resources to be affected by a single constraint.

A set of 3 resources

<resource_set id="resource-set-example">
    <resource_ref id="A"/>
    <resource_ref id="B"/>
    <resource_ref id="C"/>
</resource_set>

Resource sets are valid inside rsc_location, rsc_order (see Ordering Sets of Resources), rsc_colocation (see Colocating Sets of Resources), and rsc_ticket (see Configuring Ticket Dependencies) constraints.

A resource set has a number of properties that can be set, though not all have an effect in all contexts.

Attributes of a resource_set Element

Field Default Description
id  

A unique name for the set (required)

sequential true

Whether the members of the set must be acted on in order. Meaningful within rsc_order and rsc_colocation.

require-all true

Whether all members of the set must be active before continuing. With the current implementation, the cluster may continue even if only one member of the set is started, but if more than one member of the set is starting at the same time, the cluster will still wait until all of those have started before continuing (this may change in future versions). Meaningful within rsc_order.

role  

The constraint applies only to resource set members that are Promotable clones in this role. Meaningful within rsc_location, rsc_colocation and rsc_ticket. Allowed values: Started, Promoted, Unpromoted. For details, see Promotable Clone Constraints.

action value of first-action in the enclosing ordering constraint

The action that applies to all members of the set. Meaningful within rsc_order. Allowed values: start, stop, promote, demote.

score  

Advanced use only. Use a specific score for this set within the constraint.

5.6. Ordering Sets of Resources

A common situation is for an administrator to create a chain of ordered resources, such as:

A chain of ordered resources

<constraints>
    <rsc_order id="order-1" first="A" then="B" />
    <rsc_order id="order-2" first="B" then="C" />
    <rsc_order id="order-3" first="C" then="D" />
</constraints>

Visual representation of the four resources’ start order for the above constraints

Ordered set
5.6.1. Ordered Set

To simplify this situation, Resource Sets can be used within ordering constraints:

A chain of ordered resources expressed as a set

<constraints>
    <rsc_order id="order-1">
      <resource_set id="ordered-set-example" sequential="true">
        <resource_ref id="A"/>
        <resource_ref id="B"/>
        <resource_ref id="C"/>
        <resource_ref id="D"/>
      </resource_set>
    </rsc_order>
</constraints>

While the set-based format is not less verbose, it is significantly easier to get right and maintain.

Important

If you use a higher-level tool, pay attention to how it exposes this functionality. Depending on the tool, creating a set A B may be equivalent to A then B, or B then A.

5.6.2. Ordering Multiple Sets

The syntax can be expanded to allow sets of resources to be ordered relative to each other, where the members of each individual set may be ordered or unordered (controlled by the sequential property). In the example below, A and B can both start in parallel, as can C and D, however C and D can only start once both A and B are active.

Ordered sets of unordered resources

<constraints>
    <rsc_order id="order-1">
        <resource_set id="ordered-set-1" sequential="false">
            <resource_ref id="A"/>
            <resource_ref id="B"/>
        </resource_set>
        <resource_set id="ordered-set-2" sequential="false">
            <resource_ref id="C"/>
            <resource_ref id="D"/>
        </resource_set>
    </rsc_order>
</constraints>

Visual representation of the start order for two ordered sets of unordered resources

Two ordered sets

Of course either set – or both sets – of resources can also be internally ordered (by setting sequential="true") and there is no limit to the number of sets that can be specified.

Advanced use of set ordering - Three ordered sets, two of which are internally unordered

<constraints>
    <rsc_order id="order-1">
      <resource_set id="ordered-set-1" sequential="false">
        <resource_ref id="A"/>
        <resource_ref id="B"/>
      </resource_set>
      <resource_set id="ordered-set-2" sequential="true">
        <resource_ref id="C"/>
        <resource_ref id="D"/>
      </resource_set>
      <resource_set id="ordered-set-3" sequential="false">
        <resource_ref id="E"/>
        <resource_ref id="F"/>
      </resource_set>
    </rsc_order>
</constraints>

Visual representation of the start order for the three sets defined above

Three ordered sets

Important

An ordered set with sequential=false makes sense only if there is another set in the constraint. Otherwise, the constraint has no effect.

5.6.3. Resource Set OR Logic

The unordered set logic discussed so far has all been “AND” logic. To illustrate this take the 3 resource set figure in the previous section. Those sets can be expressed, (A and B) then (C) then (D) then (E and F).

Say for example we want to change the first set, (A and B), to use “OR” logic so the sets look like this: (A or B) then (C) then (D) then (E and F). This functionality can be achieved through the use of the require-all option. This option defaults to TRUE which is why the “AND” logic is used by default. Setting require-all=false means only one resource in the set needs to be started before continuing on to the next set.

Resource Set “OR” logic: Three ordered sets, where the first set is internally unordered with “OR” logic

<constraints>
    <rsc_order id="order-1">
      <resource_set id="ordered-set-1" sequential="false" require-all="false">
        <resource_ref id="A"/>
        <resource_ref id="B"/>
      </resource_set>
      <resource_set id="ordered-set-2" sequential="true">
        <resource_ref id="C"/>
        <resource_ref id="D"/>
      </resource_set>
      <resource_set id="ordered-set-3" sequential="false">
        <resource_ref id="E"/>
        <resource_ref id="F"/>
      </resource_set>
    </rsc_order>
</constraints>

Important

An ordered set with require-all=false makes sense only in conjunction with sequential=false. Think of it like this: sequential=false modifies the set to be an unordered set using “AND” logic by default, and adding require-all=false flips the unordered set’s “AND” logic to “OR” logic.

5.7. Colocating Sets of Resources

Another common situation is for an administrator to create a set of colocated resources.

The simplest way to do this is to define a resource group (see Groups - A Syntactic Shortcut), but that cannot always accurately express the desired relationships. For example, maybe the resources do not need to be ordered.

Another way would be to define each relationship as an individual constraint, but that causes a difficult-to-follow constraint explosion as the number of resources and combinations grow.

Colocation chain as individual constraints, where A is placed first, then B, then C, then D

<constraints>
    <rsc_colocation id="coloc-1" rsc="D" with-rsc="C" score="INFINITY"/>
    <rsc_colocation id="coloc-2" rsc="C" with-rsc="B" score="INFINITY"/>
    <rsc_colocation id="coloc-3" rsc="B" with-rsc="A" score="INFINITY"/>
</constraints>

To express complicated relationships with a simplified syntax [2], resource sets can be used within colocation constraints.

Equivalent colocation chain expressed using resource_set

<constraints>
    <rsc_colocation id="coloc-1" score="INFINITY" >
      <resource_set id="colocated-set-example" sequential="true">
        <resource_ref id="A"/>
        <resource_ref id="B"/>
        <resource_ref id="C"/>
        <resource_ref id="D"/>
      </resource_set>
    </rsc_colocation>
</constraints>

Note

Within a resource_set, the resources are listed in the order they are placed, which is the reverse of the order in which they are colocated. In the above example, resource A is placed before resource B, which is the same as saying resource B is colocated with resource A.

As with individual constraints, a resource that can’t be active prevents any resource that must be colocated with it from being active. In both of the two previous examples, if B is unable to run, then both C and by inference D must remain stopped.

Important

If you use a higher-level tool, pay attention to how it exposes this functionality. Depending on the tool, creating a set A B may be equivalent to A with B, or B with A.

Resource sets can also be used to tell the cluster that entire sets of resources must be colocated relative to each other, while the individual members within any one set may or may not be colocated relative to each other (determined by the set’s sequential property).

In the following example, resources B, C, and D will each be colocated with A (which will be placed first). A must be able to run in order for any of the resources to run, but any of B, C, or D may be stopped without affecting any of the others.

Using colocated sets to specify a shared dependency

<constraints>
    <rsc_colocation id="coloc-1" score="INFINITY" >
      <resource_set id="colocated-set-2" sequential="false">
        <resource_ref id="B"/>
        <resource_ref id="C"/>
        <resource_ref id="D"/>
      </resource_set>
      <resource_set id="colocated-set-1" sequential="true">
        <resource_ref id="A"/>
      </resource_set>
    </rsc_colocation>
</constraints>

Note

Pay close attention to the order in which resources and sets are listed. While the members of any one sequential set are placed first to last (i.e., the colocation dependency is last with first), multiple sets are placed last to first (i.e. the colocation dependency is first with last).

Important

A colocated set with sequential="false" makes sense only if there is another set in the constraint. Otherwise, the constraint has no effect.

There is no inherent limit to the number and size of the sets used. The only thing that matters is that in order for any member of one set in the constraint to be active, all members of sets listed after it must also be active (and naturally on the same node); and if a set has sequential="true", then in order for one member of that set to be active, all members listed before it must also be active.

If desired, you can restrict the dependency to instances of promotable clone resources that are in a specific role, using the set’s role property.

Colocation in which the members of the middle set have no interdependencies, and the last set listed applies only to promoted instances

<constraints>
    <rsc_colocation id="coloc-1" score="INFINITY" >
      <resource_set id="colocated-set-1" sequential="true">
        <resource_ref id="F"/>
        <resource_ref id="G"/>
      </resource_set>
      <resource_set id="colocated-set-2" sequential="false">
        <resource_ref id="C"/>
        <resource_ref id="D"/>
        <resource_ref id="E"/>
      </resource_set>
      <resource_set id="colocated-set-3" sequential="true" role="Promoted">
        <resource_ref id="A"/>
        <resource_ref id="B"/>
      </resource_set>
    </rsc_colocation>
</constraints>

Visual representation of the above example (resources are placed from left to right)

Colocation chain

Note

Unlike ordered sets, colocated sets do not use the require-all option.

[1]While the human brain is sophisticated enough to read the constraint in any order and choose the correct one depending on the situation, the cluster is not quite so smart. Yet.
[2]which is not the same as saying easy to follow

6. Fencing

6.1. What Is Fencing?

Fencing is the ability to make a node unable to run resources, even when that node is unresponsive to cluster commands.

Fencing is also known as STONITH, an acronym for “Shoot The Other Node In The Head”, since the most common fencing method is cutting power to the node. Another method is “fabric fencing”, cutting the node’s access to some capability required to run resources (such as network access or a shared disk).

6.2. Why Is Fencing Necessary?

Fencing protects your data from being corrupted by malfunctioning nodes or unintentional concurrent access to shared resources.

Fencing protects against the “split brain” failure scenario, where cluster nodes have lost the ability to reliably communicate with each other but are still able to run resources. If the cluster just assumed that uncommunicative nodes were down, then multiple instances of a resource could be started on different nodes.

The effect of split brain depends on the resource type. For example, an IP address brought up on two hosts on a network will cause packets to randomly be sent to one or the other host, rendering the IP useless. For a database or clustered file system, the effect could be much more severe, causing data corruption or divergence.

Fencing is also used when a resource cannot otherwise be stopped. If a resource fails to stop on a node, it cannot be started on a different node without risking the same type of conflict as split-brain. Fencing the original node ensures the resource can be safely started elsewhere.

Users may also configure the on-fail property of Resource Operations or the loss-policy property of ticket constraints to fence, in which case the cluster will fence the resource’s node if the operation fails or the ticket is lost.

6.3. Fence Devices

A fence device or fencing device is a special type of resource that provides the means to fence a node.

Examples of fencing devices include intelligent power switches and IPMI devices that accept SNMP commands to cut power to a node, and iSCSI controllers that allow SCSI reservations to be used to cut a node’s access to a shared disk.

Since fencing devices will be used to recover from loss of networking connectivity to other nodes, it is essential that they do not rely on the same network as the cluster itself, otherwise that network becomes a single point of failure.

Since loss of a node due to power outage is indistinguishable from loss of network connectivity to that node, it is also essential that at least one fence device for a node does not share power with that node. For example, an on-board IPMI controller that shares power with its host should not be used as the sole fencing device for that host.

Since fencing is used to isolate malfunctioning nodes, no fence device should rely on its target functioning properly. This includes, for example, devices that ssh into a node and issue a shutdown command (such devices might be suitable for testing, but never for production).

6.4. Fence Agents

A fence agent or fencing agent is a stonith-class resource agent.

The fence agent standard provides commands (such as off and reboot) that the cluster can use to fence nodes. As with other resource agent classes, this allows a layer of abstraction so that Pacemaker doesn’t need any knowledge about specific fencing technologies – that knowledge is isolated in the agent.

Pacemaker supports two fence agent standards, both inherited from no-longer-active projects:

  • Red Hat Cluster Suite (RHCS) style: These are typically installed in /usr/sbin with names starting with fence_.
  • Linux-HA style: These typically have names starting with external/. Pacemaker can support these agents using the fence_legacy RHCS-style agent as a wrapper, if support was enabled when Pacemaker was built, which requires the cluster-glue library.

6.5. When a Fence Device Can Be Used

Fencing devices do not actually “run” like most services. Typically, they just provide an interface for sending commands to an external device.

Additionally, fencing may be initiated by Pacemaker, by other cluster-aware software such as DRBD or DLM, or manually by an administrator, at any point in the cluster life cycle, including before any resources have been started.

To accommodate this, Pacemaker does not require the fence device resource to be “started” in order to be used. Whether a fence device is started or not determines whether a node runs any recurring monitor for the device, and gives the node a slight preference for being chosen to execute fencing using that device.

By default, any node can execute any fencing device. If a fence device is disabled by setting its target-role to Stopped, then no node can use that device. If a location constraint with a negative score prevents a specific node from “running” a fence device, then that node will never be chosen to execute fencing using the device. A node may fence itself, but the cluster will choose that only if no other nodes can do the fencing.

A common configuration scenario is to have one fence device per target node. In such a case, users often configure anti-location constraints so that the target node does not monitor its own device.

6.6. Limitations of Fencing Resources

Fencing resources have certain limitations that other resource classes don’t:

  • They may have only one set of meta-attributes and one set of instance attributes.
  • If Rules are used to determine fencing resource options, these might be evaluated only when first read, meaning that later changes to the rules will have no effect. Therefore, it is better to avoid confusion and not use rules at all with fencing resources.

These limitations could be revisited if there is sufficient user demand.

6.7. Special Meta-Attributes for Fencing Resources

The table below lists special resource meta-attributes that may be set for any fencing resource.

Additional Properties of Fencing Resources
Field Type Default Description
provides string  

Any special capability provided by the fence device. Currently, only one such capability is meaningful: unfencing.

6.8. Special Instance Attributes for Fencing Resources

The table below lists special instance attributes that may be set for any fencing resource (not meta-attributes, even though they are interpreted by Pacemaker rather than the fence agent). These are also listed in the man page for pacemaker-fenced.

Additional Properties of Fencing Resources
Field Type Default Description
stonith-timeout time  

This is not used by Pacemaker (see the pcmk_reboot_timeout, pcmk_off_timeout, etc. properties instead), but it may be used by Linux-HA fence agents.

pcmk_host_map string  

A mapping of node names to ports for devices that do not understand the node names.

Example: node1:1;node2:2,3 tells the cluster to use port 1 for node1 and ports 2 and 3 for node2. If pcmk_host_check is explicitly set to static-list, either this or pcmk_host_list must be set. The port portion of the map may contain special characters such as spaces if preceded by a backslash (since 2.1.2).

pcmk_host_list string  

A list of machines controlled by this device. If pcmk_host_check is explicitly set to static-list, either this or pcmk_host_map must be set.

pcmk_host_check string Value appropriate to other parameters (see “Default Check Type” below)

The method Pacemaker should use to determine which nodes can be targeted by this device. Allowed values:

  • static-list: targets are listed in the pcmk_host_list or pcmk_host_map attribute
  • dynamic-list: query the device via the agent’s list action
  • status: query the device via the agent’s status action
  • none: assume the device can fence any node
pcmk_delay_max time 0s

Enable a delay of no more than the time specified before executing fencing actions. Pacemaker derives the overall delay by taking the value of pcmk_delay_base and adding a random delay value such that the sum is kept below this maximum. This is sometimes used in two-node clusters to ensure that the nodes don’t fence each other at the same time.

pcmk_delay_base time 0s

Enable a static delay before executing fencing actions. This can be used, for example, in two-node clusters to ensure that the nodes don’t fence each other, by having separate fencing resources with different values. The node that is fenced with the shorter delay will lose a fencing race. The overall delay introduced by pacemaker is derived from this value plus a random delay such that the sum is kept below the maximum delay. A single device can have different delays per node using a host map (since 2.1.2), for example node1:0s;node2:5s.

pcmk_action_limit integer 1

The maximum number of actions that can be performed in parallel on this device. A value of -1 means unlimited. Node fencing actions initiated by the cluster (as opposed to an administrator running the stonith_admin tool or the fencer running recurring device monitors and status and list commands) are additionally subject to the concurrent-fencing cluster property.

pcmk_host_argument string port otherwise plug if supported according to the metadata of the fence agent

Advanced use only. Which parameter should be supplied to the fence agent to identify the node to be fenced. Some devices support neither the standard plug nor the deprecated port parameter, or may provide additional ones. Use this to specify an alternate, device-specific parameter. A value of none tells the cluster not to supply any additional parameters.

pcmk_reboot_action string reboot

Advanced use only. The command to send to the resource agent in order to reboot a node. Some devices do not support the standard commands or may provide additional ones. Use this to specify an alternate, device-specific command.

pcmk_reboot_timeout time 60s

Advanced use only. Specify an alternate timeout to use for reboot actions instead of the value of stonith-timeout. Some devices need much more or less time to complete than normal. Use this to specify an alternate, device-specific timeout.

pcmk_reboot_retries integer 2

Advanced use only. The maximum number of times to retry the reboot command within the timeout period. Some devices do not support multiple connections, and operations may fail if the device is busy with another task, so Pacemaker will automatically retry the operation, if there is time remaining. Use this option to alter the number of times Pacemaker retries before giving up.

pcmk_off_action string off

Advanced use only. The command to send to the resource agent in order to shut down a node. Some devices do not support the standard commands or may provide additional ones. Use this to specify an alternate, device-specific command.

pcmk_off_timeout time 60s

Advanced use only. Specify an alternate timeout to use for off actions instead of the value of stonith-timeout. Some devices need much more or less time to complete than normal. Use this to specify an alternate, device-specific timeout.

pcmk_off_retries integer 2

Advanced use only. The maximum number of times to retry the off command within the timeout period. Some devices do not support multiple connections, and operations may fail if the device is busy with another task, so Pacemaker will automatically retry the operation, if there is time remaining. Use this option to alter the number of times Pacemaker retries before giving up.

pcmk_list_action string list

Advanced use only. The command to send to the resource agent in order to list nodes. Some devices do not support the standard commands or may provide additional ones. Use this to specify an alternate, device-specific command.

pcmk_list_timeout time 60s

Advanced use only. Specify an alternate timeout to use for list actions instead of the value of stonith-timeout. Some devices need much more or less time to complete than normal. Use this to specify an alternate, device-specific timeout.

pcmk_list_retries integer 2

Advanced use only. The maximum number of times to retry the list command within the timeout period. Some devices do not support multiple connections, and operations may fail if the device is busy with another task, so Pacemaker will automatically retry the operation, if there is time remaining. Use this option to alter the number of times Pacemaker retries before giving up.

pcmk_monitor_action string monitor

Advanced use only. The command to send to the resource agent in order to report extended status. Some devices do not support the standard commands or may provide additional ones. Use this to specify an alternate, device-specific command.

pcmk_monitor_timeout time 60s

Advanced use only. Specify an alternate timeout to use for monitor actions instead of the value of stonith-timeout. Some devices need much more or less time to complete than normal. Use this to specify an alternate, device-specific timeout.

pcmk_monitor_retries integer 2

Advanced use only. The maximum number of times to retry the monitor command within the timeout period. Some devices do not support multiple connections, and operations may fail if the device is busy with another task, so Pacemaker will automatically retry the operation, if there is time remaining. Use this option to alter the number of times Pacemaker retries before giving up.

pcmk_status_action string status

Advanced use only. The command to send to the resource agent in order to report status. Some devices do not support the standard commands or may provide additional ones. Use this to specify an alternate, device-specific command.

pcmk_status_timeout time 60s

Advanced use only. Specify an alternate timeout to use for status actions instead of the value of stonith-timeout. Some devices need much more or less time to complete than normal. Use this to specify an alternate, device-specific timeout.

pcmk_status_retries integer 2

Advanced use only. The maximum number of times to retry the status command within the timeout period. Some devices do not support multiple connections, and operations may fail if the device is busy with another task, so Pacemaker will automatically retry the operation, if there is time remaining. Use this option to alter the number of times Pacemaker retries before giving up.

6.9. Default Check Type

If the user does not explicitly configure pcmk_host_check for a fence device, a default value appropriate to other configured parameters will be used:

  • If either pcmk_host_list or pcmk_host_map is configured, static-list will be used;
  • otherwise, if the fence device supports the list action, and the first attempt at using list succeeds, dynamic-list will be used;
  • otherwise, if the fence device supports the status action, status will be used;
  • otherwise, none will be used.

6.10. Unfencing

With fabric fencing (such as cutting network or shared disk access rather than power), it is expected that the cluster will fence the node, and then a system administrator must manually investigate what went wrong, correct any issues found, then reboot (or restart the cluster services on) the node.

Once the node reboots and rejoins the cluster, some fabric fencing devices require an explicit command to restore the node’s access. This capability is called unfencing and is typically implemented as the fence agent’s on command.

If any cluster resource has requires set to unfencing, then that resource will not be probed or started on a node until that node has been unfenced.

6.11. Fencing and Quorum

In general, a cluster partition may execute fencing only if the partition has quorum, and the stonith-enabled cluster property is set to true. However, there are exceptions:

  • The requirements apply only to fencing initiated by Pacemaker. If an administrator initiates fencing using the stonith_admin command, or an external application such as DLM initiates fencing using Pacemaker’s C API, the requirements do not apply.
  • A cluster partition without quorum is allowed to fence any active member of that partition. As a corollary, this allows a no-quorum-policy of suicide to work.
  • If the no-quorum-policy cluster property is set to ignore, then quorum is not required to execute fencing of any node.

6.12. Fencing Timeouts

Fencing timeouts are complicated, since a single fencing operation can involve many steps, each of which may have a separate timeout.

Fencing may be initiated in one of several ways:

  • An administrator may initiate fencing using the stonith_admin tool, which has a --timeout option (defaulting to 2 minutes) that will be used as the fence operation timeout.
  • An external application such as DLM may initiate fencing using the Pacemaker C API. The application will specify the fence operation timeout in this case, which might or might not be configurable by the user.
  • The cluster may initiate fencing itself. In this case, the stonith-timeout cluster property (defaulting to 1 minute) will be used as the fence operation timeout.

However fencing is initiated, the initiator contacts Pacemaker’s fencer (pacemaker-fenced) to request fencing. This connection and request has its own timeout, separate from the fencing operation timeout, but usually happens very quickly.

The fencer will contact all fencers in the cluster to ask what devices they have available to fence the target node. The fence operation timeout will be used as the timeout for each of these queries.

Once a fencing device has been selected, the fencer will check whether any action-specific timeout has been configured for the device, to use instead of the fence operation timeout. For example, if stonith-timeout is 60 seconds, but the fencing device has pcmk_reboot_timeout configured as 90 seconds, then a timeout of 90 seconds will be used for reboot actions using that device.

A device may have retries configured, in which case the timeout applies across all attempts. For example, if a device has pcmk_reboot_retries configured as 2, and the first reboot attempt fails, the second attempt will only have whatever time is remaining in the action timeout after subtracting how much time the first attempt used. This means that if the first attempt fails due to using the entire timeout, no further attempts will be made. There is currently no way to configure a per-attempt timeout.

If more than one device is required to fence a target, whether due to failure of the first device or a fencing topology with multiple devices configured for the target, each device will have its own separate action timeout.

For all of the above timeouts, the fencer will generally multiply the configured value by 1.2 to get an actual value to use, to account for time needed by the fencer’s own processing.

Separate from the fencer’s timeouts, some fence agents have internal timeouts for individual steps of their fencing process. These agents often have parameters to configure these timeouts, such as login-timeout, shell-timeout, or power-timeout. Many such agents also have a disable-timeout parameter to ignore their internal timeouts and just let Pacemaker handle the timeout. This causes a difference in retry behavior. If disable-timeout is not set, and the agent hits one of its internal timeouts, it will report that as a failure to Pacemaker, which can then retry. If disable-timeout is set, and Pacemaker hits a timeout for the agent, then there will be no time remaining, and no retry will be done.

6.13. Fence Devices Dependent on Other Resources

In some cases, a fence device may require some other cluster resource (such as an IP address) to be active in order to function properly.

This is obviously undesirable in general: fencing may be required when the depended-on resource is not active, or fencing may be required because the node running the depended-on resource is no longer responding.

However, this may be acceptable under certain conditions:

  • The dependent fence device should not be able to target any node that is allowed to run the depended-on resource.
  • The depended-on resource should not be disabled during production operation.
  • The concurrent-fencing cluster property should be set to true. Otherwise, if both the node running the depended-on resource and some node targeted by the dependent fence device need to be fenced, the fencing of the node running the depended-on resource might be ordered first, making the second fencing impossible and blocking further recovery. With concurrent fencing, the dependent fence device might fail at first due to the depended-on resource being unavailable, but it will be retried and eventually succeed once the resource is brought back up.

Even under those conditions, there is one unlikely problem scenario. The DC always schedules fencing of itself after any other fencing needed, to avoid unnecessary repeated DC elections. If the dependent fence device targets the DC, and both the DC and a different node running the depended-on resource need to be fenced, the DC fencing will always fail and block further recovery. Note, however, that losing a DC node entirely causes some other node to become DC and schedule the fencing, so this is only a risk when a stop or other operation with on-fail set to fencing fails on the DC.

6.14. Configuring Fencing

Higher-level tools can provide simpler interfaces to this process, but using Pacemaker command-line tools, this is how you could configure a fence device.

  1. Find the correct driver:

    # stonith_admin --list-installed
    

    Note

    You may have to install packages to make fence agents available on your host. Searching your available packages for fence- is usually helpful. Ensure the packages providing the fence agents you require are installed on every cluster node.

  2. Find the required parameters associated with the device (replacing $AGENT_NAME with the name obtained from the previous step):

    # stonith_admin --metadata --agent $AGENT_NAME
    
  3. Create a file called stonith.xml containing a primitive resource with a class of stonith, a type equal to the agent name obtained earlier, and a parameter for each of the values returned in the previous step.

  4. If the device does not know how to fence nodes based on their uname, you may also need to set the special pcmk_host_map parameter. See Special Meta-Attributes for Fencing Resources for details.

  5. If the device does not support the list command, you may also need to set the special pcmk_host_list and/or pcmk_host_check parameters. See Special Meta-Attributes for Fencing Resources for details.

  6. If the device does not expect the victim to be specified with the port parameter, you may also need to set the special pcmk_host_argument parameter. See Special Meta-Attributes for Fencing Resources for details.

  7. Upload it into the CIB using cibadmin:

    # cibadmin --create --scope resources --xml-file stonith.xml
    
  8. Set stonith-enabled to true:

    # crm_attribute --type crm_config --name stonith-enabled --update true
    
  9. Once the stonith resource is running, you can test it by executing the following, replacing $NODE_NAME with the name of the node to fence (although you might want to stop the cluster on that machine first):

    # stonith_admin --reboot $NODE_NAME
    
6.14.1. Example Fencing Configuration

For this example, we assume we have a cluster node, pcmk-1, whose IPMI controller is reachable at the IP address 192.0.2.1. The IPMI controller uses the username testuser and the password abc123.

  1. Looking at what’s installed, we may see a variety of available agents:

    # stonith_admin --list-installed
    
    (... some output omitted ...)
    fence_idrac
    fence_ilo3
    fence_ilo4
    fence_ilo5
    fence_imm
    fence_ipmilan
    (... some output omitted ...)
    

    Perhaps after some reading some man pages and doing some Internet searches, we might decide fence_ipmilan is our best choice.

  2. Next, we would check what parameters fence_ipmilan provides:

    # stonith_admin --metadata -a fence_ipmilan
    
    <resource-agent name="fence_ipmilan" shortdesc="Fence agent for IPMI">
      <symlink name="fence_ilo3" shortdesc="Fence agent for HP iLO3"/>
      <symlink name="fence_ilo4" shortdesc="Fence agent for HP iLO4"/>
      <symlink name="fence_ilo5" shortdesc="Fence agent for HP iLO5"/>
      <symlink name="fence_imm" shortdesc="Fence agent for IBM Integrated Management Module"/>
      <symlink name="fence_idrac" shortdesc="Fence agent for Dell iDRAC"/>
      <longdesc>fence_ipmilan is an I/O Fencing agentwhich can be used with machines controlled by IPMI.This agent calls support software ipmitool (http://ipmitool.sf.net/). WARNING! This fence agent might report success before the node is powered off. You should use -m/method onoff if your fence device works correctly with that option.</longdesc>
      <vendor-url/>
      <parameters>
        <parameter name="action" unique="0" required="0">
          <getopt mixed="-o, --action=[action]"/>
          <content type="string" default="reboot"/>
          <shortdesc lang="en">Fencing action</shortdesc>
        </parameter>
        <parameter name="auth" unique="0" required="0">
          <getopt mixed="-A, --auth=[auth]"/>
          <content type="select">
            <option value="md5"/>
            <option value="password"/>
            <option value="none"/>
          </content>
          <shortdesc lang="en">IPMI Lan Auth type.</shortdesc>
        </parameter>
        <parameter name="cipher" unique="0" required="0">
          <getopt mixed="-C, --cipher=[cipher]"/>
          <content type="string"/>
          <shortdesc lang="en">Ciphersuite to use (same as ipmitool -C parameter)</shortdesc>
        </parameter>
        <parameter name="hexadecimal_kg" unique="0" required="0">
          <getopt mixed="--hexadecimal-kg=[key]"/>
          <content type="string"/>
          <shortdesc lang="en">Hexadecimal-encoded Kg key for IPMIv2 authentication</shortdesc>
        </parameter>
        <parameter name="ip" unique="0" required="0" obsoletes="ipaddr">
          <getopt mixed="-a, --ip=[ip]"/>
          <content type="string"/>
          <shortdesc lang="en">IP address or hostname of fencing device</shortdesc>
        </parameter>
        <parameter name="ipaddr" unique="0" required="0" deprecated="1">
          <getopt mixed="-a, --ip=[ip]"/>
          <content type="string"/>
          <shortdesc lang="en">IP address or hostname of fencing device</shortdesc>
        </parameter>
        <parameter name="ipport" unique="0" required="0">
          <getopt mixed="-u, --ipport=[port]"/>
          <content type="integer" default="623"/>
          <shortdesc lang="en">TCP/UDP port to use for connection with device</shortdesc>
        </parameter>
        <parameter name="lanplus" unique="0" required="0">
          <getopt mixed="-P, --lanplus"/>
          <content type="boolean" default="0"/>
          <shortdesc lang="en">Use Lanplus to improve security of connection</shortdesc>
        </parameter>
        <parameter name="login" unique="0" required="0" deprecated="1">
          <getopt mixed="-l, --username=[name]"/>
          <content type="string"/>
          <shortdesc lang="en">Login name</shortdesc>
        </parameter>
        <parameter name="method" unique="0" required="0">
          <getopt mixed="-m, --method=[method]"/>
          <content type="select" default="onoff">
            <option value="onoff"/>
            <option value="cycle"/>
          </content>
          <shortdesc lang="en">Method to fence</shortdesc>
        </parameter>
        <parameter name="passwd" unique="0" required="0" deprecated="1">
          <getopt mixed="-p, --password=[password]"/>
          <content type="string"/>
          <shortdesc lang="en">Login password or passphrase</shortdesc>
        </parameter>
        <parameter name="passwd_script" unique="0" required="0" deprecated="1">
          <getopt mixed="-S, --password-script=[script]"/>
          <content type="string"/>
          <shortdesc lang="en">Script to run to retrieve password</shortdesc>
        </parameter>
        <parameter name="password" unique="0" required="0" obsoletes="passwd">
          <getopt mixed="-p, --password=[password]"/>
          <content type="string"/>
          <shortdesc lang="en">Login password or passphrase</shortdesc>
        </parameter>
        <parameter name="password_script" unique="0" required="0" obsoletes="passwd_script">
          <getopt mixed="-S, --password-script=[script]"/>
          <content type="string"/>
          <shortdesc lang="en">Script to run to retrieve password</shortdesc>
        </parameter>
        <parameter name="plug" unique="0" required="0" obsoletes="port">
          <getopt mixed="-n, --plug=[ip]"/>
          <content type="string"/>
          <shortdesc lang="en">IP address or hostname of fencing device (together with --port-as-ip)</shortdesc>
        </parameter>
        <parameter name="port" unique="0" required="0" deprecated="1">
          <getopt mixed="-n, --plug=[ip]"/>
          <content type="string"/>
          <shortdesc lang="en">IP address or hostname of fencing device (together with --port-as-ip)</shortdesc>
        </parameter>
        <parameter name="privlvl" unique="0" required="0">
          <getopt mixed="-L, --privlvl=[level]"/>
          <content type="select" default="administrator">
            <option value="callback"/>
            <option value="user"/>
            <option value="operator"/>
            <option value="administrator"/>
          </content>
          <shortdesc lang="en">Privilege level on IPMI device</shortdesc>
        </parameter>
        <parameter name="target" unique="0" required="0">
          <getopt mixed="--target=[targetaddress]"/>
          <content type="string"/>
          <shortdesc lang="en">Bridge IPMI requests to the remote target address</shortdesc>
        </parameter>
        <parameter name="username" unique="0" required="0" obsoletes="login">
          <getopt mixed="-l, --username=[name]"/>
          <content type="string"/>
          <shortdesc lang="en">Login name</shortdesc>
        </parameter>
        <parameter name="quiet" unique="0" required="0">
          <getopt mixed="-q, --quiet"/>
          <content type="boolean"/>
          <shortdesc lang="en">Disable logging to stderr. Does not affect --verbose or --debug-file or logging to syslog.</shortdesc>
        </parameter>
        <parameter name="verbose" unique="0" required="0">
          <getopt mixed="-v, --verbose"/>
          <content type="boolean"/>
          <shortdesc lang="en">Verbose mode</shortdesc>
        </parameter>
        <parameter name="debug" unique="0" required="0" deprecated="1">
          <getopt mixed="-D, --debug-file=[debugfile]"/>
          <content type="string"/>
          <shortdesc lang="en">Write debug information to given file</shortdesc>
        </parameter>
        <parameter name="debug_file" unique="0" required="0" obsoletes="debug">
          <getopt mixed="-D, --debug-file=[debugfile]"/>
          <content type="string"/>
          <shortdesc lang="en">Write debug information to given file</shortdesc>
        </parameter>
        <parameter name="version" unique="0" required="0">
          <getopt mixed="-V, --version"/>
          <content type="boolean"/>
          <shortdesc lang="en">Display version information and exit</shortdesc>
        </parameter>
        <parameter name="help" unique="0" required="0">
          <getopt mixed="-h, --help"/>
          <content type="boolean"/>
          <shortdesc lang="en">Display help and exit</shortdesc>
        </parameter>
        <parameter name="delay" unique="0" required="0">
          <getopt mixed="--delay=[seconds]"/>
          <content type="second" default="0"/>
          <shortdesc lang="en">Wait X seconds before fencing is started</shortdesc>
        </parameter>
        <parameter name="ipmitool_path" unique="0" required="0">
          <getopt mixed="--ipmitool-path=[path]"/>
          <content type="string" default="/usr/bin/ipmitool"/>
          <shortdesc lang="en">Path to ipmitool binary</shortdesc>
        </parameter>
        <parameter name="login_timeout" unique="0" required="0">
          <getopt mixed="--login-timeout=[seconds]"/>
          <content type="second" default="5"/>
          <shortdesc lang="en">Wait X seconds for cmd prompt after login</shortdesc>
        </parameter>
        <parameter name="port_as_ip" unique="0" required="0">
          <getopt mixed="--port-as-ip"/>
          <content type="boolean"/>
          <shortdesc lang="en">Make "port/plug" to be an alias to IP address</shortdesc>
        </parameter>
        <parameter name="power_timeout" unique="0" required="0">
          <getopt mixed="--power-timeout=[seconds]"/>
          <content type="second" default="20"/>
          <shortdesc lang="en">Test X seconds for status change after ON/OFF</shortdesc>
        </parameter>
        <parameter name="power_wait" unique="0" required="0">
          <getopt mixed="--power-wait=[seconds]"/>
          <content type="second" default="2"/>
          <shortdesc lang="en">Wait X seconds after issuing ON/OFF</shortdesc>
        </parameter>
        <parameter name="shell_timeout" unique="0" required="0">
          <getopt mixed="--shell-timeout=[seconds]"/>
          <content type="second" default="3"/>
          <shortdesc lang="en">Wait X seconds for cmd prompt after issuing command</shortdesc>
        </parameter>
        <parameter name="retry_on" unique="0" required="0">
          <getopt mixed="--retry-on=[attempts]"/>
          <content type="integer" default="1"/>
          <shortdesc lang="en">Count of attempts to retry power on</shortdesc>
        </parameter>
        <parameter name="sudo" unique="0" required="0" deprecated="1">
          <getopt mixed="--use-sudo"/>
          <content type="boolean"/>
          <shortdesc lang="en">Use sudo (without password) when calling 3rd party software</shortdesc>
        </parameter>
        <parameter name="use_sudo" unique="0" required="0" obsoletes="sudo">
          <getopt mixed="--use-sudo"/>
          <content type="boolean"/>
          <shortdesc lang="en">Use sudo (without password) when calling 3rd party software</shortdesc>
        </parameter>
        <parameter name="sudo_path" unique="0" required="0">
          <getopt mixed="--sudo-path=[path]"/>
          <content type="string" default="/usr/bin/sudo"/>
          <shortdesc lang="en">Path to sudo binary</shortdesc>
        </parameter>
      </parameters>
      <actions>
        <action name="on" automatic="0"/>
        <action name="off"/>
        <action name="reboot"/>
        <action name="status"/>
        <action name="monitor"/>
        <action name="metadata"/>
        <action name="manpage"/>
        <action name="validate-all"/>
        <action name="diag"/>
        <action name="stop" timeout="20s"/>
        <action name="start" timeout="20s"/>
      </actions>
    </resource-agent>
    

    Once we’ve decided what parameter values we think we need, it is a good idea to run the fence agent’s status action manually, to verify that our values work correctly:

    # fence_ipmilan --lanplus -a 192.0.2.1 -l testuser -p abc123 -o status
    
    Chassis Power is on
    
  3. Based on that, we might create a fencing resource configuration like this in stonith.xml (or any file name, just use the same name with cibadmin later):

    <primitive id="Fencing-pcmk-1" class="stonith" type="fence_ipmilan" >
      <instance_attributes id="Fencing-params" >
        <nvpair id="Fencing-lanplus" name="lanplus" value="1" />
        <nvpair id="Fencing-ip" name="ip" value="192.0.2.1" />
        <nvpair id="Fencing-password" name="password" value="testuser" />
        <nvpair id="Fencing-username" name="username" value="abc123" />
      </instance_attributes>
      <operations >
        <op id="Fencing-monitor-10m" interval="10m" name="monitor" timeout="300s" />
      </operations>
    </primitive>
    

    Note

    Even though the man page shows that the action parameter is supported, we do not provide that in the resource configuration. Pacemaker will supply an appropriate action whenever the fence device must be used.

  4. In this case, we don’t need to configure pcmk_host_map because fence_ipmilan ignores the target node name and instead uses its ip parameter to know how to contact the IPMI controller.

  5. We do need to let Pacemaker know which cluster node can be fenced by this device, since fence_ipmilan doesn’t support the list action. Add a line like this to the agent’s instance attributes:

    <nvpair id="Fencing-pcmk_host_list" name="pcmk_host_list" value="pcmk-1" />
    
  6. We don’t need to configure pcmk_host_argument since ip is all the fence agent needs (it ignores the target name).

  7. Make the configuration active:

    # cibadmin --create --scope resources --xml-file stonith.xml
    
  8. Set stonith-enabled to true (this only has to be done once):

    # crm_attribute --type crm_config --name stonith-enabled --update true
    
  9. Since our cluster is still in testing, we can reboot pcmk-1 without bothering anyone, so we’ll test our fencing configuration by running this from one of the other cluster nodes:

    # stonith_admin --reboot pcmk-1
    

    Then we will verify that the node did, in fact, reboot.

We can repeat that process to create a separate fencing resource for each node.

With some other fence device types, a single fencing resource is able to be used for all nodes. In fact, we could do that with fence_ipmilan, using the port-as-ip parameter along with pcmk_host_map. Either approach is fine.

6.15. Fencing Topologies

Pacemaker supports fencing nodes with multiple devices through a feature called fencing topologies. Fencing topologies may be used to provide alternative devices in case one fails, or to require multiple devices to all be executed successfully in order to consider the node successfully fenced, or even a combination of the two.

Create the individual devices as you normally would, then define one or more fencing-level entries in the fencing-topology section of the configuration.

  • Each fencing level is attempted in order of ascending index. Allowed values are 1 through 9.
  • If a device fails, processing terminates for the current level. No further devices in that level are exercised, and the next level is attempted instead.
  • If the operation succeeds for all the listed devices in a level, the level is deemed to have passed.
  • The operation is finished when a level has passed (success), or all levels have been attempted (failed).
  • If the operation failed, the next step is determined by the scheduler and/or the controller.

Some possible uses of topologies include:

  • Try on-board IPMI, then an intelligent power switch if that fails
  • Try fabric fencing of both disk and network, then fall back to power fencing if either fails
  • Wait up to a certain time for a kernel dump to complete, then cut power to the node
Attributes of a fencing-level Element
Attribute Description
id

A unique name for this element (required)

target

The name of a single node to which this level applies

target-pattern

An extended regular expression (as defined in POSIX) matching the names of nodes to which this level applies

target-attribute

The name of a node attribute that is set (to target-value) for nodes to which this level applies

target-value

The node attribute value (of target-attribute) that is set for nodes to which this level applies

index

The order in which to attempt the levels. Levels are attempted in ascending order until one succeeds. Valid values are 1 through 9.

devices

A comma-separated list of devices that must all be tried for this level

Note

Fencing topology with different devices for different nodes

<cib crm_feature_set="3.6.0" validate-with="pacemaker-3.5" admin_epoch="1" epoch="0" num_updates="0">
  <configuration>
    ...
    <fencing-topology>
      <!-- For pcmk-1, try poison-pill and fail back to power -->
      <fencing-level id="f-p1.1" target="pcmk-1" index="1" devices="poison-pill"/>
      <fencing-level id="f-p1.2" target="pcmk-1" index="2" devices="power"/>

      <!-- For pcmk-2, try disk and network, and fail back to power -->
      <fencing-level id="f-p2.1" target="pcmk-2" index="1" devices="disk,network"/>
      <fencing-level id="f-p2.2" target="pcmk-2" index="2" devices="power"/>
    </fencing-topology>
    ...
  <configuration>
  <status/>
</cib>
6.15.1. Example Dual-Layer, Dual-Device Fencing Topologies

The following example illustrates an advanced use of fencing-topology in a cluster with the following properties:

  • 2 nodes (prod-mysql1 and prod-mysql2)
  • the nodes have IPMI controllers reachable at 192.0.2.1 and 192.0.2.2
  • the nodes each have two independent Power Supply Units (PSUs) connected to two independent Power Distribution Units (PDUs) reachable at 198.51.100.1 (port 10 and port 11) and 203.0.113.1 (port 10 and port 11)
  • fencing via the IPMI controller uses the fence_ipmilan agent (1 fence device per controller, with each device targeting a separate node)
  • fencing via the PDUs uses the fence_apc_snmp agent (1 fence device per PDU, with both devices targeting both nodes)
  • a random delay is used to lessen the chance of a “death match”
  • fencing topology is set to try IPMI fencing first then dual PDU fencing if that fails

In a node failure scenario, Pacemaker will first select fence_ipmilan to try to kill the faulty node. Using the fencing topology, if that method fails, it will then move on to selecting fence_apc_snmp twice (once for the first PDU, then again for the second PDU).

The fence action is considered successful only if both PDUs report the required status. If any of them fails, fencing loops back to the first fencing method, fence_ipmilan, and so on, until the node is fenced or the fencing action is cancelled.

Note

First fencing method: single IPMI device per target

Each cluster node has it own dedicated IPMI controller that can be contacted for fencing using the following primitives:

<primitive class="stonith" id="fence_prod-mysql1_ipmi" type="fence_ipmilan">
  <instance_attributes id="fence_prod-mysql1_ipmi-instance_attributes">
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-ipaddr" name="ipaddr" value="192.0.2.1"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-login" name="login" value="fencing"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-passwd" name="passwd" value="finishme"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-lanplus" name="lanplus" value="true"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql1"/>
    <nvpair id="fence_prod-mysql1_ipmi-instance_attributes-pcmk_delay_max" name="pcmk_delay_max" value="8s"/>
  </instance_attributes>
</primitive>
<primitive class="stonith" id="fence_prod-mysql2_ipmi" type="fence_ipmilan">
  <instance_attributes id="fence_prod-mysql2_ipmi-instance_attributes">
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-ipaddr" name="ipaddr" value="192.0.2.2"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-login" name="login" value="fencing"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-passwd" name="passwd" value="finishme"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-lanplus" name="lanplus" value="true"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="prod-mysql2"/>
    <nvpair id="fence_prod-mysql2_ipmi-instance_attributes-pcmk_delay_max" name="pcmk_delay_max" value="8s"/>
  </instance_attributes>
</primitive>

Note

Second fencing method: dual PDU devices

Each cluster node also has 2 distinct power supplies controlled by 2 distinct PDUs:

  • Node 1: PDU 1 port 10 and PDU 2 port 10
  • Node 2: PDU 1 port 11 and PDU 2 port 11

The matching fencing agents are configured as follows:

<primitive class="stonith" id="fence_apc1" type="fence_apc_snmp">
  <instance_attributes id="fence_apc1-instance_attributes">
    <nvpair id="fence_apc1-instance_attributes-ipaddr" name="ipaddr" value="198.51.100.1"/>
    <nvpair id="fence_apc1-instance_attributes-login" name="login" value="fencing"/>
    <nvpair id="fence_apc1-instance_attributes-passwd" name="passwd" value="fencing"/>
    <nvpair id="fence_apc1-instance_attributes-pcmk_host_list"
       name="pcmk_host_map" value="prod-mysql1:10;prod-mysql2:11"/>
    <nvpair id="fence_apc1-instance_attributes-pcmk_delay_max" name="pcmk_delay_max" value="8s"/>
  </instance_attributes>
</primitive>
<primitive class="stonith" id="fence_apc2" type="fence_apc_snmp">
  <instance_attributes id="fence_apc2-instance_attributes">
    <nvpair id="fence_apc2-instance_attributes-ipaddr" name="ipaddr" value="203.0.113.1"/>
    <nvpair id="fence_apc2-instance_attributes-login" name="login" value="fencing"/>
    <nvpair id="fence_apc2-instance_attributes-passwd" name="passwd" value="fencing"/>
    <nvpair id="fence_apc2-instance_attributes-pcmk_host_list"
       name="pcmk_host_map" value="prod-mysql1:10;prod-mysql2:11"/>
    <nvpair id="fence_apc2-instance_attributes-pcmk_delay_max" name="pcmk_delay_max" value="8s"/>
  </instance_attributes>
</primitive>

Note

Fencing topology

Now that all the fencing resources are defined, it’s time to create the right topology. We want to first fence using IPMI and if that does not work, fence both PDUs to effectively and surely kill the node.

<fencing-topology>
  <fencing-level id="level-1-1" target="prod-mysql1" index="1" devices="fence_prod-mysql1_ipmi" />
  <fencing-level id="level-1-2" target="prod-mysql1" index="2" devices="fence_apc1,fence_apc2"  />
  <fencing-level id="level-2-1" target="prod-mysql2" index="1" devices="fence_prod-mysql2_ipmi" />
  <fencing-level id="level-2-2" target="prod-mysql2" index="2" devices="fence_apc1,fence_apc2"  />
</fencing-topology>

In fencing-topology, the lowest index value for a target determines its first fencing method.

6.16. Remapping Reboots

When the cluster needs to reboot a node, whether because stonith-action is reboot or because a reboot was requested externally (such as by stonith_admin --reboot), it will remap that to other commands in two cases:

  • If the chosen fencing device does not support the reboot command, the cluster will ask it to perform off instead.
  • If a fencing topology level with multiple devices must be executed, the cluster will ask all the devices to perform off, then ask the devices to perform on.

To understand the second case, consider the example of a node with redundant power supplies connected to intelligent power switches. Rebooting one switch and then the other would have no effect on the node. Turning both switches off, and then on, actually reboots the node.

In such a case, the fencing operation will be treated as successful as long as the off commands succeed, because then it is safe for the cluster to recover any resources that were on the node. Timeouts and errors in the on phase will be logged but ignored.

When a reboot operation is remapped, any action-specific timeout for the remapped action will be used (for example, pcmk_off_timeout will be used when executing the off command, not pcmk_reboot_timeout).

7. Alerts

Alerts may be configured to take some external action when a cluster event occurs (node failure, resource starting or stopping, etc.).

7.1. Alert Agents

As with resource agents, the cluster calls an external program (an alert agent) to handle alerts. The cluster passes information about the event to the agent via environment variables. Agents can do anything desired with this information (send an e-mail, log to a file, update a monitoring system, etc.).

Simple alert configuration

<configuration>
   <alerts>
      <alert id="my-alert" path="/path/to/my-script.sh" />
   </alerts>
</configuration>

In the example above, the cluster will call my-script.sh for each event.

Multiple alert agents may be configured; the cluster will call all of them for each event.

Alert agents will be called only on cluster nodes. They will be called for events involving Pacemaker Remote nodes, but they will never be called on those nodes.

7.2. Alert Recipients

Usually, alerts are directed towards a recipient. Thus, each alert may be additionally configured with one or more recipients. The cluster will call the agent separately for each recipient.

Alert configuration with recipient

<configuration>
   <alerts>
      <alert id="my-alert" path="/path/to/my-script.sh">
          <recipient id="my-alert-recipient" value="some-address"/>
      </alert>
   </alerts>
</configuration>

In the above example, the cluster will call my-script.sh for each event, passing the recipient some-address as an environment variable.

The recipient may be anything the alert agent can recognize – an IP address, an e-mail address, a file name, whatever the particular agent supports.

7.3. Alert Meta-Attributes

As with resource agents, meta-attributes can be configured for alert agents to affect how Pacemaker calls them.

Meta-Attributes of an Alert
Meta-Attribute Default Description
timestamp-format %H:%M:%S.%06N

Format the cluster will use when sending the event’s timestamp to the agent. This is a string as used with the date(1) command.

timeout 30s

If the alert agent does not complete within this amount of time, it will be terminated.

Meta-attributes can be configured per alert agent and/or per recipient.

Alert configuration with meta-attributes

<configuration>
   <alerts>
      <alert id="my-alert" path="/path/to/my-script.sh">
         <meta_attributes id="my-alert-attributes">
            <nvpair id="my-alert-attributes-timeout" name="timeout"
                    value="15s"/>
         </meta_attributes>
         <recipient id="my-alert-recipient1" value="someuser@example.com">
            <meta_attributes id="my-alert-recipient1-attributes">
               <nvpair id="my-alert-recipient1-timestamp-format"
                       name="timestamp-format" value="%D %H:%M"/>
            </meta_attributes>
         </recipient>
         <recipient id="my-alert-recipient2" value="otheruser@example.com">
            <meta_attributes id="my-alert-recipient2-attributes">
               <nvpair id="my-alert-recipient2-timestamp-format"
                       name="timestamp-format" value="%c"/>
            </meta_attributes>
         </recipient>
      </alert>
   </alerts>
</configuration>

In the above example, the my-script.sh will get called twice for each event, with each call using a 15-second timeout. One call will be passed the recipient someuser@example.com and a timestamp in the format %D %H:%M, while the other call will be passed the recipient otheruser@example.com and a timestamp in the format %c.

7.4. Alert Instance Attributes

As with resource agents, agent-specific configuration values may be configured as instance attributes. These will be passed to the agent as additional environment variables. The number, names and allowed values of these instance attributes are completely up to the particular agent.

Alert configuration with instance attributes

<configuration>
   <alerts>
      <alert id="my-alert" path="/path/to/my-script.sh">
         <meta_attributes id="my-alert-attributes">
            <nvpair id="my-alert-attributes-timeout" name="timeout"
                    value="15s"/>
         </meta_attributes>
         <instance_attributes id="my-alert-options">
             <nvpair id="my-alert-options-debug" name="debug"
                     value="false"/>
         </instance_attributes>
         <recipient id="my-alert-recipient1"
                    value="someuser@example.com"/>
      </alert>
   </alerts>
</configuration>

7.5. Alert Filters

By default, an alert agent will be called for node events, fencing events, and resource events. An agent may choose to ignore certain types of events, but there is still the overhead of calling it for those events. To eliminate that overhead, you may select which types of events the agent should receive.

Alert configuration to receive only node events and fencing events

<configuration>
   <alerts>
      <alert id="my-alert" path="/path/to/my-script.sh">
         <select>
            <select_nodes />
            <select_fencing />
         </select>
         <recipient id="my-alert-recipient1"
                    value="someuser@example.com"/>
      </alert>
   </alerts>
</configuration>

The possible options within <select> are <select_nodes>, <select_fencing>, <select_resources>, and <select_attributes>.

With <select_attributes> (the only event type not enabled by default), the agent will receive alerts when a node attribute changes. If you wish the agent to be called only when certain attributes change, you can configure that as well.

Alert configuration to be called when certain node attributes change

<configuration>
   <alerts>
      <alert id="my-alert" path="/path/to/my-script.sh">
         <select>
            <select_attributes>
               <attribute id="alert-standby" name="standby" />
               <attribute id="alert-shutdown" name="shutdown" />
            </select_attributes>
         </select>
         <recipient id="my-alert-recipient1" value="someuser@example.com"/>
      </alert>
   </alerts>
</configuration>

Node attribute alerts are currently considered experimental. Alerts may be limited to attributes set via attrd_updater, and agents may be called multiple times with the same attribute value.

7.6. Using the Sample Alert Agents

Pacemaker provides several sample alert agents, installed in /usr/share/pacemaker/alerts by default.

While these sample scripts may be copied and used as-is, they are provided mainly as templates to be edited to suit your purposes. See their source code for the full set of instance attributes they support.

Sending cluster events as SNMP traps

<configuration>
   <alerts>
      <alert id="snmp_alert" path="/path/to/alert_snmp.sh">
         <instance_attributes id="config_for_alert_snmp">
            <nvpair id="trap_node_states" name="trap_node_states"
                    value="all"/>
         </instance_attributes>
         <meta_attributes id="config_for_timestamp">
            <nvpair id="ts_fmt" name="timestamp-format"
                    value="%Y-%m-%d,%H:%M:%S.%01N"/>
         </meta_attributes>
         <recipient id="snmp_destination" value="192.168.1.2"/>
      </alert>
   </alerts>
</configuration>

Sending cluster events as e-mails

<configuration>
   <alerts>
      <alert id="smtp_alert" path="/path/to/alert_smtp.sh">
         <instance_attributes id="config_for_alert_smtp">
            <nvpair id="email_sender" name="email_sender"
                    value="donotreply@example.com"/>
         </instance_attributes>
         <recipient id="smtp_destination" value="admin@example.com"/>
      </alert>
   </alerts>
</configuration>

7.7. Writing an Alert Agent

Environment variables passed to alert agents
Environment Variable Description
CRM_alert_kind

The type of alert (node, fencing, resource, or attribute)

CRM_alert_node

Name of affected node

CRM_alert_node_sequence

A sequence number increased whenever an alert is being issued on the local node, which can be used to reference the order in which alerts have been issued by Pacemaker. An alert for an event that happened later in time reliably has a higher sequence number than alerts for earlier events.

Be aware that this number has no cluster-wide meaning.

CRM_alert_recipient

The configured recipient

CRM_alert_timestamp

A timestamp created prior to executing the agent, in the format specified by the timestamp-format meta-attribute. This allows the agent to have a reliable, high-precision time of when the event occurred, regardless of when the agent itself was invoked (which could potentially be delayed due to system load, etc.).

CRM_alert_timestamp_epoch

The same time as CRM_alert_timestamp, expressed as the integer number of seconds since January 1, 1970. This (along with CRM_alert_timestamp_usec) can be useful for alert agents that need to format time in a specific way rather than let the user configure it.

CRM_alert_timestamp_usec

The same time as CRM_alert_timestamp, expressed as the integer number of microseconds since CRM_alert_timestamp_epoch.

CRM_alert_version

The version of Pacemaker sending the alert

CRM_alert_desc

Detail about event. For node alerts, this is the node’s current state (member or lost). For fencing alerts, this is a summary of the requested fencing operation, including origin, target, and fencing operation error code, if any. For resource alerts, this is a readable string equivalent of CRM_alert_status.

CRM_alert_nodeid

ID of node whose status changed (provided with node alerts only)

CRM_alert_rc

The numerical return code of the fencing or resource operation (provided with fencing and resource alerts only)

CRM_alert_task

The requested fencing or resource operation (provided with fencing and resource alerts only)

CRM_alert_exec_time

The (wall-clock) time, in milliseconds, that it took to execute the action. If the action timed out, CRM_alert_status will be 2, CRM_alert_desc will be “Timed Out”, and this value will be the action timeout. May not be supported on all platforms. (resource alerts only) (since 2.0.1)

CRM_alert_interval

The interval of the resource operation (resource alerts only)

CRM_alert_rsc

The name of the affected resource (resource alerts only)

CRM_alert_status

A numerical code used by Pacemaker to represent the operation result (resource alerts only)

CRM_alert_target_rc

The expected numerical return code of the operation (resource alerts only)

CRM_alert_attribute_name

The name of the node attribute that changed (attribute alerts only)

CRM_alert_attribute_value

The new value of the node attribute that changed (attribute alerts only)

Special concerns when writing alert agents:

  • Alert agents may be called with no recipient (if none is configured), so the agent must be able to handle this situation, even if it only exits in that case. (Users may modify the configuration in stages, and add a recipient later.)
  • If more than one recipient is configured for an alert, the alert agent will be called once per recipient. If an agent is not able to run concurrently, it should be configured with only a single recipient. The agent is free, however, to interpret the recipient as a list.
  • When a cluster event occurs, all alerts are fired off at the same time as separate processes. Depending on how many alerts and recipients are configured, and on what is done within the alert agents, a significant load burst may occur. The agent could be written to take this into consideration, for example by queueing resource-intensive actions into some other instance, instead of directly executing them.
  • Alert agents are run as the hacluster user, which has a minimal set of permissions. If an agent requires additional privileges, it is recommended to configure sudo to allow the agent to run the necessary commands as another user with the appropriate privileges.
  • As always, take care to validate and sanitize user-configured parameters, such as CRM_alert_timestamp (whose content is specified by the user-configured timestamp-format), CRM_alert_recipient, and all instance attributes. Mostly this is needed simply to protect against configuration errors, but if some user can modify the CIB without having hacluster-level access to the cluster nodes, it is a potential security concern as well, to avoid the possibility of code injection.

Note

ocf:pacemaker:ClusterMon compatibility

The alerts interface is designed to be backward compatible with the external scripts interface used by the ocf:pacemaker:ClusterMon resource, which is now deprecated. To preserve this compatibility, the environment variables passed to alert agents are available prepended with CRM_notify_ as well as CRM_alert_. One break in compatibility is that ClusterMon ran external scripts as the root user, while alert agents are run as the hacluster user.

8. Rules

Rules can be used to make your configuration more dynamic, allowing values to change depending on the time or the value of a node attribute. Examples of things rules are useful for:

  • Set a higher value for resource-stickiness during working hours, to minimize downtime, and a lower value on weekends, to allow resources to move to their most preferred locations when people aren’t around to notice.
  • Automatically place the cluster into maintenance mode during a scheduled maintenance window.
  • Assign certain nodes and resources to a particular department via custom node attributes and meta-attributes, and add a single location constraint that restricts the department’s resources to run only on those nodes.

Each constraint type or property set that supports rules may contain one or more rule elements specifying conditions under which the constraint or properties take effect. Examples later in this chapter will make this clearer.

8.1. Rule Properties

Attributes of a rule Element
Attribute Default Description
id  

A unique name for this element (required)

role Started

The rule is in effect only when the resource is in the specified role. Allowed values are Started, Unpromoted, and Promoted. A rule with a role of Promoted cannot determine the initial location of a clone instance and will only affect which of the active instances will be promoted.

score  

If this rule is used in a location constraint and evaluates to true, apply this score to the constraint. Only one of score and score-attribute may be used.

score-attribute  

If this rule is used in a location constraint and evaluates to true, use the value of this node attribute as the score to apply to the constraint. Only one of score and score-attribute may be used.

boolean-op and

If this rule contains more than one condition, a value of and specifies that the rule evaluates to true only if all conditions are true, and a value of or specifies that the rule evaluates to true if any condition is true.

A rule element must contain one or more conditions. A condition may be an expression element, a date_expression element, or another rule element.

8.2. Node Attribute Expressions

Expressions are rule conditions based on the values of node attributes.

Attributes of an expression Element
Attribute Default Description
id  

A unique name for this element (required)

attribute  

The node attribute to test (required)

type The default type for lt, gt, lte, and gte operations is number if either value contains a decimal point character, or integer otherwise. The default type for all other operations is string. If a numeric parse fails for either value, then the values are compared as type string.

How the node attributes should be compared. Allowed values are string, integer (since 2.0.5), number, and version. integer truncates floating-point values if necessary before performing a 64-bit integer comparison. number performs a double-precision floating-point comparison (32-bit integer before 2.0.5).

operation  

The comparison to perform (required). Allowed values:

  • lt: True if the node attribute value
    is less than the comparison value
  • gt: True if the node attribute value
    is greater than the comparison value
  • lte: True if the node attribute
    value is less than or equal to the comparison value
  • gte: True if the node attribute
    value is greater than or equal to the comparison value
  • eq: True if the node attribute value
    is equal to the comparison value
  • ne: True if the node attribute value
    is not equal to the comparison value
  • defined: True if the node has the
    named attribute
  • not_defined: True if the node does
    not have the named attribute
value  

User-supplied value for comparison (required for operations other than defined and not_defined)

value-source literal

How the value is derived. Allowed values:

  • literal: value is a literal string to compare against
  • param: value is the name of a resource parameter to compare against (only valid in location constraints)
  • meta: value is the name of a resource meta-attribute to compare against (only valid in location constraints)

In addition to custom node attributes defined by the administrator, the cluster defines special, built-in node attributes for each node that can also be used in rule expressions.

Built-in Node Attributes
Name Value
#uname Node name
#id Node ID
#kind Node type. Possible values are cluster, remote, and container. Kind is remote for Pacemaker Remote nodes created with the ocf:pacemaker:remote resource, and container for Pacemaker Remote guest nodes and bundle nodes
#is_dc true if this node is the cluster’s Designated Controller (DC), false otherwise
#cluster-name The value of the cluster-name cluster property, if set
#site-name The value of the site-name node attribute, if set, otherwise identical to #cluster-name
#role The role the relevant promotable clone resource has on this node. Valid only within a rule for a location constraint for a promotable clone resource.

8.3. Date/Time Expressions

Date/time expressions are rule conditions based (as the name suggests) on the current date and time.

A date_expression element may optionally contain a date_spec or duration element depending on the context.

Attributes of a date_expression Element
Attribute Description
id

A unique name for this element (required)

start

A date/time conforming to the ISO8601 specification. May be used when operation is in_range (in which case at least one of start or end must be specified) or gt (in which case start is required).

end A date/time conforming to the ISO8601 specification. May be used when operation is in_range (in which case at least one of start or end must be specified) or lt (in which case end is required).
operation

Compares the current date/time with the start and/or end date, depending on the context. Allowed values:

  • gt: True if the current date/time is after start
  • lt: True if the current date/time is before end
  • in_range: True if the current date/time is after start (if specified) and before either end (if specified) or start plus the value of the duration element (if one is contained in the date_expression)
  • date_spec: True if the current date/time matches the specification given in the contained date_spec element (described below)

Note

There is no eq, neq, gte, or lte operation, since they would be valid only for a single second.

8.3.1. Date Specifications

A date_spec element is used to create a cron-like expression relating to time. Each field can contain a single number or range. Any field not supplied is ignored.

Attributes of a date_spec Element
Attribute Description
id

A unique name for this element (required)

hours

Allowed values: 0-23 (where 0 is midnight and 23 is 11 p.m.)

monthdays

Allowed values: 1-31 (depending on month and year)

weekdays

Allowed values: 1-7 (where 1 is Monday and 7 is Sunday)

yeardays

Allowed values: 1-366 (depending on the year)

months

Allowed values: 1-12

weeks

Allowed values: 1-53 (depending on weekyear)

years

Year according to the Gregorian calendar

weekyears

Year in which the week started; for example, 1 January 2005 can be specified in ISO 8601 as “2005-001 Ordinal”, “2005-01-01 Gregorian” or “2004-W53-6 Weekly” and thus would match years="2005" or weekyears="2004"

moon

Allowed values are 0-7 (where 0 is the new moon and 4 is full moon). Seriously, you can use this. This was implemented to demonstrate the ease with which new comparisons could be added.

For example, monthdays="1" matches the first day of every month, and hours="09-17" matches the hours between 9 a.m. and 5 p.m. (inclusive).

At this time, multiple ranges (e.g. weekdays="1,2" or weekdays="1-2,5-6") are not supported.

Note

Pacemaker can calculate when evaluation of a date_expression with an operation of gt, lt, or in_range will next change, and schedule a cluster re-check for that time. However, it does not do this for date_spec. Instead, it evaluates the date_spec whenever a cluster re-check naturally happens via a cluster event or the cluster-recheck-interval cluster option.

For example, if you have a date_spec enabling a resource from 9 a.m. to 5 p.m., and cluster-recheck-interval has been set to 5 minutes, then sometime between 9 a.m. and 9:05 a.m. the cluster would notice that it needs to start the resource, and sometime between 5 p.m. and 5:05 p.m. it would realize that it needs to stop the resource. The timing of the actual start and stop actions will further depend on factors such as any other actions the cluster may need to perform first, and the load of the machine.

8.3.2. Durations

A duration is used to calculate a value for end when one is not supplied to in_range operations. It contains one or more attributes each containing a single number. Any attribute not supplied is ignored.

Attributes of a duration Element
Attribute Description
id

A unique name for this element (required)

seconds

This many seconds will be added to the total duration

minutes

This many minutes will be added to the total duration

hours

This many hours will be added to the total duration

weeks

This many weeks will be added to the total duration

months

This many months will be added to the total duration

years

This many years will be added to the total duration

8.3.3. Example Time-Based Expressions

A small sample of how time-based expressions can be used:

True if now is any time in the year 2005

<rule id="rule1" score="INFINITY">
   <date_expression id="date_expr1" start="2005-001" operation="in_range">
    <duration id="duration1" years="1"/>
   </date_expression>
</rule>

or equivalently:

<rule id="rule2" score="INFINITY">
   <date_expression id="date_expr2" operation="date_spec">
    <date_spec id="date_spec2" years="2005"/>
   </date_expression>
</rule>

9 a.m. to 5 p.m. Monday through Friday

<rule id="rule3" score="INFINITY">
   <date_expression id="date_expr3" operation="date_spec">
    <date_spec id="date_spec3" hours="9-16" weekdays="1-5"/>
   </date_expression>
</rule>

Note that the 16 matches all the way through 16:59:59, because the numeric value of the hour still matches.

9 a.m. to 6 p.m. Monday through Friday or anytime Saturday

<rule id="rule4" score="INFINITY" boolean-op="or">
   <date_expression id="date_expr4-1" operation="date_spec">
    <date_spec id="date_spec4-1" hours="9-16" weekdays="1-5"/>
   </date_expression>
   <date_expression id="date_expr4-2" operation="date_spec">
    <date_spec id="date_spec4-2" weekdays="6"/>
   </date_expression>
</rule>

9 a.m. to 5 p.m. or 9 p.m. to 12 a.m. Monday through Friday

<rule id="rule5" score="INFINITY" boolean-op="and">
   <rule id="rule5-nested1" score="INFINITY" boolean-op="or">
    <date_expression id="date_expr5-1" operation="date_spec">
     <date_spec id="date_spec5-1" hours="9-16"/>
    </date_expression>
    <date_expression id="date_expr5-2" operation="date_spec">
     <date_spec id="date_spec5-2" hours="21-23"/>
    </date_expression>
   </rule>
   <date_expression id="date_expr5-3" operation="date_spec">
    <date_spec id="date_spec5-3" weekdays="1-5"/>
   </date_expression>
</rule>

Mondays in March 2005

<rule id="rule6" score="INFINITY" boolean-op="and">
   <date_expression id="date_expr6-1" operation="date_spec">
    <date_spec id="date_spec6" weekdays="1"/>
   </date_expression>
   <date_expression id="date_expr6-2" operation="in_range"
     start="2005-03-01" end="2005-04-01"/>
</rule>

Note

Because no time is specified with the above dates, 00:00:00 is implied. This means that the range includes all of 2005-03-01 but none of 2005-04-01. You may wish to write end as "2005-03-31T23:59:59" to avoid confusion.

A full moon on Friday the 13th

<rule id="rule7" score="INFINITY" boolean-op="and">
   <date_expression id="date_expr7" operation="date_spec">
    <date_spec id="date_spec7" weekdays="5" monthdays="13" moon="4"/>
   </date_expression>
</rule>

8.4. Resource Expressions

An rsc_expression (since 2.0.5) is a rule condition based on a resource agent’s properties. This rule is only valid within an rsc_defaults or op_defaults context. None of the matching attributes of class, provider, and type are required. If one is omitted, all values of that attribute will match. For instance, omitting type means every type will match.

Attributes of a rsc_expression Element
Attribute Description
id

A unique name for this element (required)

class

The standard name to be matched against resource agents

provider

If given, the vendor to be matched against resource agents (only relevant when class is ocf)

type

The name of the resource agent to be matched

8.4.1. Example Resource-Based Expressions

A small sample of how resource-based expressions can be used:

True for all ocf:heartbeat:IPaddr2 resources

<rule id="rule1" score="INFINITY">
    <rsc_expression id="rule_expr1" class="ocf" provider="heartbeat" type="IPaddr2"/>
</rule>

Provider doesn’t apply to non-OCF resources

<rule id="rule2" score="INFINITY">
    <rsc_expression id="rule_expr2" class="stonith" type="fence_xvm"/>
</rule>

8.5. Operation Expressions

An op_expression (since 2.0.5) is a rule condition based on an action of some resource agent. This rule is only valid within an op_defaults context.

Attributes of an op_expression Element
Attribute Description
id

A unique name for this element (required)

name

The action name to match against. This can be any action supported by the resource agent; common values include monitor, start, and stop (required).

interval

The interval of the action to match against. If not given, only the name attribute will be used to match.

8.5.1. Example Operation-Based Expressions

A small sample of how operation-based expressions can be used:

True for all monitor actions

<rule id="rule1" score="INFINITY">
    <op_expression id="rule_expr1" name="monitor"/>
</rule>

True for all monitor actions with a 10 second interval

<rule id="rule2" score="INFINITY">
    <op_expression id="rule_expr2" name="monitor" interval="10s"/>
</rule>

8.6. Using Rules to Determine Resource Location

A location constraint may contain one or more top-level rules. The cluster will act as if there is a separate location constraint for each rule that evaluates as true.

Consider the following simple location constraint:

Prevent resource webserver from running on node node3

<rsc_location id="ban-apache-on-node3" rsc="webserver"
              score="-INFINITY" node="node3"/>

The same constraint can be more verbosely written using a rule:

Prevent resource webserver from running on node node3 using a rule

<rsc_location id="ban-apache-on-node3" rsc="webserver">
    <rule id="ban-apache-rule" score="-INFINITY">
      <expression id="ban-apache-expr" attribute="#uname"
        operation="eq" value="node3"/>
    </rule>
</rsc_location>

The advantage of using the expanded form is that one could add more expressions (for example, limiting the constraint to certain days of the week), or activate the constraint by some node attribute other than node name.

8.6.1. Location Rules Based on Other Node Properties

The expanded form allows us to match on node properties other than its name. If we rated each machine’s CPU power such that the cluster had the following nodes section:

Sample node section with node attributes

<nodes>
   <node id="uuid1" uname="c001n01" type="normal">
      <instance_attributes id="uuid1-custom_attrs">
        <nvpair id="uuid1-cpu_mips" name="cpu_mips" value="1234"/>
      </instance_attributes>
   </node>
   <node id="uuid2" uname="c001n02" type="normal">
      <instance_attributes id="uuid2-custom_attrs">
        <nvpair id="uuid2-cpu_mips" name="cpu_mips" value="5678"/>
      </instance_attributes>
   </node>
</nodes>

then we could prevent resources from running on underpowered machines with this rule:

Rule using a node attribute (to be used inside a location constraint)

<rule id="need-more-power-rule" score="-INFINITY">
   <expression id="need-more-power-expr" attribute="cpu_mips"
               operation="lt" value="3000"/>
</rule>
8.6.2. Using score-attribute Instead of score

When using score-attribute instead of score, each node matched by the rule has its score adjusted differently, according to its value for the named node attribute. Thus, in the previous example, if a rule inside a location constraint for a resource used score-attribute="cpu_mips", c001n01 would have its preference to run the resource increased by 1234 whereas c001n02 would have its preference increased by 5678.

8.7. Using Rules to Define Options

Rules may be used to control a variety of options:

  • Cluster options (cluster_property_set elements)
  • Node attributes (instance_attributes or utilization elements inside a node element)
  • Resource options (utilization, meta_attributes, or instance_attributes elements inside a resource definition element or op , rsc_defaults, op_defaults, or template element)
  • Operation properties (meta_attributes elements inside an op or op_defaults element)

Note

Attribute-based expressions for meta-attributes can only be used within operations and op_defaults. They will not work with resource configuration or rsc_defaults. Additionally, attribute-based expressions cannot be used with cluster options.

8.7.1. Using Rules to Control Resource Options

Often some cluster nodes will be different from their peers. Sometimes, these differences – e.g. the location of a binary or the names of network interfaces – require resources to be configured differently depending on the machine they’re hosted on.

By defining multiple instance_attributes objects for the resource and adding a rule to each, we can easily handle these special cases.

In the example below, mySpecialRsc will use eth1 and port 9999 when run on node1, eth2 and port 8888 on node2 and default to eth0 and port 9999 for all other nodes.

Defining different resource options based on the node name

<primitive id="mySpecialRsc" class="ocf" type="Special" provider="me">
   <instance_attributes id="special-node1" score="3">
    <rule id="node1-special-case" score="INFINITY" >
     <expression id="node1-special-case-expr" attribute="#uname"
       operation="eq" value="node1"/>
    </rule>
    <nvpair id="node1-interface" name="interface" value="eth1"/>
   </instance_attributes>
   <instance_attributes id="special-node2" score="2" >
    <rule id="node2-special-case" score="INFINITY">
     <expression id="node2-special-case-expr" attribute="#uname"
       operation="eq" value="node2"/>
    </rule>
    <nvpair id="node2-interface" name="interface" value="eth2"/>
    <nvpair id="node2-port" name="port" value="8888"/>
   </instance_attributes>
   <instance_attributes id="defaults" score="1" >
    <nvpair id="default-interface" name="interface" value="eth0"/>
    <nvpair id="default-port" name="port" value="9999"/>
   </instance_attributes>
</primitive>

The order in which instance_attributes objects are evaluated is determined by their score (highest to lowest). If not supplied, the score defaults to zero. Objects with an equal score are processed in their listed order. If the instance_attributes object has no rule, or a rule that evaluates to true, then for any parameter the resource does not yet have a value for, the resource will use the parameter values defined by the instance_attributes.

For example, given the configuration above, if the resource is placed on node1:

  • special-node1 has the highest score (3) and so is evaluated first; its rule evaluates to true, so interface is set to eth1.
  • special-node2 is evaluated next with score 2, but its rule evaluates to false, so it is ignored.
  • defaults is evaluated last with score 1, and has no rule, so its values are examined; interface is already defined, so the value here is not used, but port is not yet defined, so port is set to 9999.
8.7.2. Using Rules to Control Resource Defaults

Rules can be used for resource and operation defaults. The following example illustrates how to set a different resource-stickiness value during and outside work hours. This allows resources to automatically move back to their most preferred hosts, but at a time that (in theory) does not interfere with business activities.

Change resource-stickiness during working hours

<rsc_defaults>
   <meta_attributes id="core-hours" score="2">
      <rule id="core-hour-rule" score="0">
        <date_expression id="nine-to-five-Mon-to-Fri" operation="date_spec">
          <date_spec id="nine-to-five-Mon-to-Fri-spec" hours="9-16" weekdays="1-5"/>
        </date_expression>
      </rule>
      <nvpair id="core-stickiness" name="resource-stickiness" value="INFINITY"/>
   </meta_attributes>
   <meta_attributes id="after-hours" score="1" >
      <nvpair id="after-stickiness" name="resource-stickiness" value="0"/>
   </meta_attributes>
</rsc_defaults>

Rules may be used similarly in instance_attributes or utilization blocks.

Any single block may directly contain only a single rule, but that rule may itself contain any number of rules.

rsc_expression and op_expression blocks may additionally be used to set defaults on either a single resource or across an entire class of resources with a single rule. rsc_expression may be used to select resource agents within both rsc_defaults and op_defaults, while op_expression may only be used within op_defaults. If multiple rules succeed for a given resource agent, the last one specified will be the one that takes effect. As with any other rule, boolean operations may be used to make more complicated expressions.

Default all IPaddr2 resources to stopped

<rsc_defaults>
    <meta_attributes id="op-target-role">
        <rule id="op-target-role-rule" score="INFINITY">
            <rsc_expression id="op-target-role-expr" class="ocf" provider="heartbeat"
              type="IPaddr2"/>
        </rule>
        <nvpair id="op-target-role-nvpair" name="target-role" value="Stopped"/>
    </meta_attributes>
</rsc_defaults>

Default all monitor action timeouts to 7 seconds

<op_defaults>
    <meta_attributes id="op-monitor-defaults">
        <rule id="op-monitor-default-rule" score="INFINITY">
            <op_expression id="op-monitor-default-expr" name="monitor"/>
        </rule>
        <nvpair id="op-monitor-timeout" name="timeout" value="7s"/>
    </meta_attributes>
</op_defaults>

Default the timeout on all 10-second-interval monitor actions on IPaddr2 resources to 8 seconds

<op_defaults>
    <meta_attributes id="op-monitor-and">
        <rule id="op-monitor-and-rule" score="INFINITY">
            <rsc_expression id="op-monitor-and-rsc-expr" class="ocf" provider="heartbeat"
              type="IPaddr2"/>
            <op_expression id="op-monitor-and-op-expr" name="monitor" interval="10s"/>
        </rule>
        <nvpair id="op-monitor-and-timeout" name="timeout" value="8s"/>
    </meta_attributes>
</op_defaults>
8.7.3. Using Rules to Control Cluster Options

Controlling cluster options is achieved in much the same manner as specifying different resource options on different nodes.

The following example illustrates how to set maintenance_mode during a scheduled maintenance window. This will keep the cluster running but not monitor, start, or stop resources during this time.

Schedule a maintenance window for 9 to 11 p.m. CDT Sept. 20, 2019

<crm_config>
   <cluster_property_set id="cib-bootstrap-options">
     <nvpair id="bootstrap-stonith-enabled" name="stonith-enabled" value="1"/>
   </cluster_property_set>
   <cluster_property_set id="normal-set" score="10">
     <nvpair id="normal-maintenance-mode" name="maintenance-mode" value="false"/>
   </cluster_property_set>
   <cluster_property_set id="maintenance-window-set" score="1000">
     <nvpair id="maintenance-nvpair1" name="maintenance-mode" value="true"/>
     <rule id="maintenance-rule1" score="INFINITY">
       <date_expression id="maintenance-date1" operation="in_range"
         start="2019-09-20 21:00:00 -05:00" end="2019-09-20 23:00:00 -05:00"/>
     </rule>
   </cluster_property_set>
</crm_config>

Important

The cluster_property_set with an id set to “cib-bootstrap-options” will always have the highest priority, regardless of any scores. Therefore, rules in another cluster_property_set can never take effect for any properties listed in the bootstrap set.

9. Advanced Configuration

9.1. Specifying When Recurring Actions are Performed

By default, recurring actions are scheduled relative to when the resource started. In some cases, you might prefer that a recurring action start relative to a specific date and time. For example, you might schedule an in-depth monitor to run once every 24 hours, and want it to run outside business hours.

To do this, set the operation’s interval-origin. The cluster uses this point to calculate the correct start-delay such that the operation will occur at interval-origin plus a multiple of the operation interval.

For example, if the recurring operation’s interval is 24h, its interval-origin is set to 02:00, and it is currently 14:32, then the cluster would initiate the operation after 11 hours and 28 minutes.

The value specified for interval and interval-origin can be any date/time conforming to the ISO8601 standard. By way of example, to specify an operation that would run on the first Monday of 2021 and every Monday after that, you would add:

Example recurring action that runs relative to base date/time

<op id="intensive-monitor" name="monitor" interval="P7D" interval-origin="2021-W01-1"/>

9.2. Handling Resource Failure

By default, Pacemaker will attempt to recover failed resources by restarting them. However, failure recovery is highly configurable.

9.2.1. Failure Counts

Pacemaker tracks resource failures for each combination of node, resource, and operation (start, stop, monitor, etc.).

You can query the fail count for a particular node, resource, and/or operation using the crm_failcount command. For example, to see how many times the 10-second monitor for myrsc has failed on node1, run:

# crm_failcount --query -r myrsc -N node1 -n monitor -I 10s

If you omit the node, crm_failcount will use the local node. If you omit the operation and interval, crm_failcount will display the sum of the fail counts for all operations on the resource.

You can use crm_resource --cleanup or crm_failcount --delete to clear fail counts. For example, to clear the above monitor failures, run:

# crm_resource --cleanup -r myrsc -N node1 -n monitor -I 10s

If you omit the resource, crm_resource --cleanup will clear failures for all resources. If you omit the node, it will clear failures on all nodes. If you omit the operation and interval, it will clear the failures for all operations on the resource.

Note

Even when cleaning up only a single operation, all failed operations will disappear from the status display. This allows us to trigger a re-check of the resource’s current status.

Higher-level tools may provide other commands for querying and clearing fail counts.

The crm_mon tool shows the current cluster status, including any failed operations. To see the current fail counts for any failed resources, call crm_mon with the --failcounts option. This shows the fail counts per resource (that is, the sum of any operation fail counts for the resource).

9.2.2. Failure Response

Normally, if a running resource fails, pacemaker will try to stop it and start it again. Pacemaker will choose the best location to start it each time, which may be the same node that it failed on.

However, if a resource fails repeatedly, it is possible that there is an underlying problem on that node, and you might desire trying a different node in such a case. Pacemaker allows you to set your preference via the migration-threshold resource meta-attribute. [1]

If you define migration-threshold to N for a resource, it will be banned from the original node after N failures there.

Note

The migration-threshold is per resource, even though fail counts are tracked per operation. The operation fail counts are added together to compare against the migration-threshold.

By default, fail counts remain until manually cleared by an administrator using crm_resource --cleanup or crm_failcount --delete (hopefully after first fixing the failure’s cause). It is possible to have fail counts expire automatically by setting the failure-timeout resource meta-attribute.

Important

A successful operation does not clear past failures. If a recurring monitor operation fails once, succeeds many times, then fails again days later, its fail count is 2. Fail counts are cleared only by manual intervention or falure timeout.

For example, setting migration-threshold to 2 and failure-timeout to 60s would cause the resource to move to a new node after 2 failures, and allow it to move back (depending on stickiness and constraint scores) after one minute.

Note

failure-timeout is measured since the most recent failure. That is, older failures do not individually time out and lower the fail count. Instead, all failures are timed out simultaneously (and the fail count is reset to 0) if there is no new failure for the timeout period.

There are two exceptions to the migration threshold: when a resource either fails to start or fails to stop.

If the cluster property start-failure-is-fatal is set to true (which is the default), start failures cause the fail count to be set to INFINITY and thus always cause the resource to move immediately.

Stop failures are slightly different and crucial. If a resource fails to stop and fencing is enabled, then the cluster will fence the node in order to be able to start the resource elsewhere. If fencing is disabled, then the cluster has no way to continue and will not try to start the resource elsewhere, but will try to stop it again after any failure timeout or clearing.

9.3. Moving Resources

9.3.1. Moving Resources Manually

There are primarily two occasions when you would want to move a resource from its current location: when the whole node is under maintenance, and when a single resource needs to be moved.

9.3.1.1. Standby Mode

Since everything eventually comes down to a score, you could create constraints for every resource to prevent them from running on one node. While Pacemaker configuration can seem convoluted at times, not even we would require this of administrators.

Instead, you can set a special node attribute which tells the cluster “don’t let anything run here”. There is even a helpful tool to help query and set it, called crm_standby. To check the standby status of the current machine, run:

# crm_standby -G

A value of on indicates that the node is not able to host any resources, while a value of off says that it can.

You can also check the status of other nodes in the cluster by specifying the –node option:

# crm_standby -G --node sles-2

To change the current node’s standby status, use -v instead of -G:

# crm_standby -v on

Again, you can change another host’s value by supplying a hostname with --node.

A cluster node in standby mode will not run resources, but still contributes to quorum, and may fence or be fenced by nodes.

9.3.1.2. Moving One Resource

When only one resource is required to move, we could do this by creating location constraints. However, once again we provide a user-friendly shortcut as part of the crm_resource command, which creates and modifies the extra constraints for you. If Email were running on sles-1 and you wanted it moved to a specific location, the command would look something like:

# crm_resource -M -r Email -H sles-2

Behind the scenes, the tool will create the following location constraint:

<rsc_location id="cli-prefer-Email" rsc="Email" node="sles-2" score="INFINITY"/>

It is important to note that subsequent invocations of crm_resource -M are not cumulative. So, if you ran these commands:

# crm_resource -M -r Email -H sles-2
# crm_resource -M -r Email -H sles-3

then it is as if you had never performed the first command.

To allow the resource to move back again, use:

# crm_resource -U -r Email

Note the use of the word allow. The resource can move back to its original location, but depending on resource-stickiness, location constraints, and so forth, it might stay where it is.

To be absolutely certain that it moves back to sles-1, move it there before issuing the call to crm_resource -U:

# crm_resource -M -r Email -H sles-1
# crm_resource -U -r Email

Alternatively, if you only care that the resource should be moved from its current location, try:

# crm_resource -B -r Email

which will instead create a negative constraint, like:

<rsc_location id="cli-ban-Email-on-sles-1" rsc="Email" node="sles-1" score="-INFINITY"/>

This will achieve the desired effect, but will also have long-term consequences. As the tool will warn you, the creation of a -INFINITY constraint will prevent the resource from running on that node until crm_resource -U is used. This includes the situation where every other cluster node is no longer available!

In some cases, such as when resource-stickiness is set to INFINITY, it is possible that you will end up with the problem described in What if Two Nodes Have the Same Score. The tool can detect some of these cases and deals with them by creating both positive and negative constraints. For example:

<rsc_location id="cli-ban-Email-on-sles-1" rsc="Email" node="sles-1" score="-INFINITY"/>
<rsc_location id="cli-prefer-Email" rsc="Email" node="sles-2" score="INFINITY"/>

which has the same long-term consequences as discussed earlier.

9.3.2. Moving Resources Due to Connectivity Changes

You can configure the cluster to move resources when external connectivity is lost in two steps.

9.3.2.1. Tell Pacemaker to Monitor Connectivity

First, add an ocf:pacemaker:ping resource to the cluster. The ping resource uses the system utility of the same name to a test whether a list of machines (specified by DNS hostname or IP address) are reachable, and uses the results to maintain a node attribute.

The node attribute is called pingd by default, but is customizable in order to allow multiple ping groups to be defined.

Normally, the ping resource should run on all cluster nodes, which means that you’ll need to create a clone. A template for this can be found below, along with a description of the most interesting parameters.

Commonly Used ocf:pacemaker:ping Resource Parameters
Resource Parameter Description
dampen

The time to wait (dampening) for further changes to occur. Use this to prevent a resource from bouncing around the cluster when cluster nodes notice the loss of connectivity at slightly different times.

multiplier

The number of connected ping nodes gets multiplied by this value to get a score. Useful when there are multiple ping nodes configured.

host_list

The machines to contact in order to determine the current connectivity status. Allowed values include resolvable DNS connectivity host names, IPv4 addresses, and IPv6 addresses.

Example ping resource that checks node connectivity once every minute

<clone id="Connected">
   <primitive id="ping" class="ocf" provider="pacemaker" type="ping">
    <instance_attributes id="ping-attrs">
      <nvpair id="ping-dampen"     name="dampen" value="5s"/>
      <nvpair id="ping-multiplier" name="multiplier" value="1000"/>
      <nvpair id="ping-hosts"      name="host_list" value="my.gateway.com www.bigcorp.com"/>
    </instance_attributes>
    <operations>
      <op id="ping-monitor-60s" interval="60s" name="monitor"/>
    </operations>
   </primitive>
</clone>

Important

You’re only half done. The next section deals with telling Pacemaker how to deal with the connectivity status that ocf:pacemaker:ping is recording.

9.3.2.2. Tell Pacemaker How to Interpret the Connectivity Data

Important

Before attempting the following, make sure you understand Rules.

There are a number of ways to use the connectivity data.

The most common setup is for people to have a single ping target (for example, the service network’s default gateway), to prevent the cluster from running a resource on any unconnected node.

Don’t run a resource on unconnected nodes

<rsc_location id="WebServer-no-connectivity" rsc="Webserver">
   <rule id="ping-exclude-rule" score="-INFINITY" >
      <expression id="ping-exclude" attribute="pingd" operation="not_defined"/>
   </rule>
</rsc_location>

A more complex setup is to have a number of ping targets configured. You can require the cluster to only run resources on nodes that can connect to all (or a minimum subset) of them.

Run only on nodes connected to three or more ping targets

<primitive id="ping" provider="pacemaker" class="ocf" type="ping">
... <!-- omitting some configuration to highlight important parts -->
   <nvpair id="ping-multiplier" name="multiplier" value="1000"/>
...
</primitive>
...
<rsc_location id="WebServer-connectivity" rsc="Webserver">
   <rule id="ping-prefer-rule" score="-INFINITY" >
      <expression id="ping-prefer" attribute="pingd" operation="lt" value="3000"/>
   </rule>
</rsc_location>

Alternatively, you can tell the cluster only to prefer nodes with the best connectivity, by using score-attribute in the rule. Just be sure to set multiplier to a value higher than that of resource-stickiness (and don’t set either of them to INFINITY).

Prefer node with most connected ping nodes

<rsc_location id="WebServer-connectivity" rsc="Webserver">
   <rule id="ping-prefer-rule" score-attribute="pingd" >
      <expression id="ping-prefer" attribute="pingd" operation="defined"/>
   </rule>
</rsc_location>

It is perhaps easier to think of this in terms of the simple constraints that the cluster translates it into. For example, if sles-1 is connected to all five ping nodes but sles-2 is only connected to two, then it would be as if you instead had the following constraints in your configuration:

How the cluster translates the above location constraint

<rsc_location id="ping-1" rsc="Webserver" node="sles-1" score="5000"/>
<rsc_location id="ping-2" rsc="Webserver" node="sles-2" score="2000"/>

The advantage is that you don’t have to manually update any constraints whenever your network connectivity changes.

You can also combine the concepts above into something even more complex. The example below shows how you can prefer the node with the most connected ping nodes provided they have connectivity to at least three (again assuming that multiplier is set to 1000).

More complex example of choosing location based on connectivity

<rsc_location id="WebServer-connectivity" rsc="Webserver">
   <rule id="ping-exclude-rule" score="-INFINITY" >
      <expression id="ping-exclude" attribute="pingd" operation="lt" value="3000"/>
   </rule>
   <rule id="ping-prefer-rule" score-attribute="pingd" >
      <expression id="ping-prefer" attribute="pingd" operation="defined"/>
   </rule>
</rsc_location>
9.3.3. Migrating Resources

Normally, when the cluster needs to move a resource, it fully restarts the resource (that is, it stops the resource on the current node and starts it on the new node).

However, some types of resources, such as many virtual machines, are able to move to another location without loss of state (often referred to as live migration or hot migration). In pacemaker, this is called resource migration. Pacemaker can be configured to migrate a resource when moving it, rather than restarting it.

Not all resources are able to migrate; see the migration checklist below. Even those that can, won’t do so in all situations. Conceptually, there are two requirements from which the other prerequisites follow:

  • The resource must be active and healthy at the old location; and
  • everything required for the resource to run must be available on both the old and new locations.

The cluster is able to accommodate both push and pull migration models by requiring the resource agent to support two special actions: migrate_to (performed on the current location) and migrate_from (performed on the destination).

In push migration, the process on the current location transfers the resource to the new location where is it later activated. In this scenario, most of the work would be done in the migrate_to action and, if anything, the activation would occur during migrate_from.

Conversely for pull, the migrate_to action is practically empty and migrate_from does most of the work, extracting the relevant resource state from the old location and activating it.

There is no wrong or right way for a resource agent to implement migration, as long as it works.

Migration Checklist

  • The resource may not be a clone.
  • The resource agent standard must be OCF.
  • The resource must not be in a failed or degraded state.
  • The resource agent must support migrate_to and migrate_from actions, and advertise them in its meta-data.
  • The resource must have the allow-migrate meta-attribute set to true (which is not the default).

If an otherwise migratable resource depends on another resource via an ordering constraint, there are special situations in which it will be restarted rather than migrated.

For example, if the resource depends on a clone, and at the time the resource needs to be moved, the clone has instances that are stopping and instances that are starting, then the resource will be restarted. The scheduler is not yet able to model this situation correctly and so takes the safer (if less optimal) path.

Also, if a migratable resource depends on a non-migratable resource, and both need to be moved, the migratable resource will be restarted.

9.4. Tracking Node Health

A node may be functioning adequately as far as cluster membership is concerned, and yet be “unhealthy” in some respect that makes it an undesirable location for resources. For example, a disk drive may be reporting SMART errors, or the CPU may be highly loaded.

Pacemaker offers a way to automatically move resources off unhealthy nodes.

9.4.1. Node Health Attributes

Pacemaker will treat any node attribute whose name starts with #health as an indicator of node health. Node health attributes may have one of the following values:

Allowed Values for Node Health Attributes
Value Intended significance
red

This indicator is unhealthy

yellow

This indicator is becoming unhealthy

green

This indicator is healthy

integer

A numeric score to apply to all resources on this node (0 or positive is healthy, negative is unhealthy)

9.4.2. Node Health Strategy

Pacemaker assigns a node health score to each node, as the sum of the values of all its node health attributes. This score will be used as a location constraint applied to this node for all resources.

The node-health-strategy cluster option controls how Pacemaker responds to changes in node health attributes, and how it translates red, yellow, and green to scores.

Allowed values are:

Node Health Strategies
Value Effect
none

Do not track node health attributes at all.

migrate-on-red

Assign the value of -INFINITY to red, and 0 to yellow and green. This will cause all resources to move off the node if any attribute is red.

only-green

Assign the value of -INFINITY to red and yellow, and 0 to green. This will cause all resources to move off the node if any attribute is red or yellow.

progressive

Assign the value of the node-health-red cluster option to red, the value of node-health-yellow to yellow, and the value of node-health-green to green. Each node is additionally assigned a score of node-health-base (this allows resources to start even if some attributes are yellow). This strategy gives the administrator finer control over how important each value is.

custom

Track node health attributes using the same values as progressive for red, yellow, and green, but do not take them into account. The administrator is expected to implement a policy by defining Rules referencing node health attributes.

9.4.3. Configuring Node Health Agents

Since Pacemaker calculates node health based on node attributes, any method that sets node attributes may be used to measure node health. The most common are resource agents and custom daemons.

Pacemaker provides examples that can be used directly or as a basis for custom code. The ocf:pacemaker:HealthCPU, ocf:pacemaker:HealthIOWait, and ocf:pacemaker:HealthSMART resource agents set node health attributes based on CPU and disk status.

To take advantage of this feature, add the resource to your cluster (generally as a cloned resource with a recurring monitor action, to continually check the health of all nodes). For example:

Example HealthIOWait resource configuration

<clone id="resHealthIOWait-clone">
  <primitive class="ocf" id="HealthIOWait" provider="pacemaker" type="HealthIOWait">
    <instance_attributes id="resHealthIOWait-instance_attributes">
      <nvpair id="resHealthIOWait-instance_attributes-red_limit" name="red_limit" value="30"/>
      <nvpair id="resHealthIOWait-instance_attributes-yellow_limit" name="yellow_limit" value="10"/>
    </instance_attributes>
    <operations>
      <op id="resHealthIOWait-monitor-interval-5" interval="5" name="monitor" timeout="5"/>
      <op id="resHealthIOWait-start-interval-0s" interval="0s" name="start" timeout="10s"/>
      <op id="resHealthIOWait-stop-interval-0s" interval="0s" name="stop" timeout="10s"/>
    </operations>
  </primitive>
</clone>

The resource agents use attrd_updater to set proper status for each node running this resource, as a node attribute whose name starts with #health (for HealthIOWait, the node attribute is named #health-iowait).

When a node is no longer faulty, you can force the cluster to make it available to take resources without waiting for the next monitor, by setting the node health attribute to green. For example:

Force node1 to be marked as healthy

# attrd_updater --name "#health-iowait" --update "green" --node "node1"

9.5. Reloading an Agent After a Definition Change

The cluster automatically detects changes to the configuration of active resources. The cluster’s normal response is to stop the service (using the old definition) and start it again (with the new definition). This works, but some resource agents are smarter and can be told to use a new set of options without restarting.

To take advantage of this capability, the resource agent must:

  • Implement the reload-agent action. What it should do depends completely on your application!

    Note

    Resource agents may also implement a reload action to make the managed service reload its own native configuration. This is different from reload-agent, which makes effective changes in the resource’s Pacemaker configuration (specifically, the values of the agent’s reloadable parameters).

  • Advertise the reload-agent operation in the actions section of its meta-data.

  • Set the reloadable attribute to 1 in the parameters section of its meta-data for any parameters eligible to be reloaded after a change.

Once these requirements are satisfied, the cluster will automatically know to reload the resource (instead of restarting) when a reloadable parameter changes.

Note

Metadata will not be re-read unless the resource needs to be started. If you edit the agent of an already active resource to set a parameter reloadable, the resource may restart the first time the parameter value changes.

Note

If both a reloadable and non-reloadable parameter are changed simultaneously, the resource will be restarted.

Footnotes

[1]The naming of this option was perhaps unfortunate as it is easily confused with live migration, the process of moving a resource from one node to another without stopping it. Xen virtual guests are the most common example of resources that can be migrated in this manner.

10. Advanced Resource Types

10.1. Groups - A Syntactic Shortcut

One of the most common elements of a cluster is a set of resources that need to be located together, start sequentially, and stop in the reverse order. To simplify this configuration, we support the concept of groups.

A group of two primitive resources

<group id="shortcut">
   <primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
    <instance_attributes id="params-public-ip">
       <nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
    </instance_attributes>
   </primitive>
   <primitive id="Email" class="lsb" type="exim"/>
</group>

Although the example above contains only two resources, there is no limit to the number of resources a group can contain. The example is also sufficient to explain the fundamental properties of a group:

  • Resources are started in the order they appear in (Public-IP first, then Email)
  • Resources are stopped in the reverse order to which they appear in (Email first, then Public-IP)

If a resource in the group can’t run anywhere, then nothing after that is allowed to run, too.

  • If Public-IP can’t run anywhere, neither can Email;
  • but if Email can’t run anywhere, this does not affect Public-IP in any way

The group above is logically equivalent to writing:

How the cluster sees a group resource

<configuration>
   <resources>
    <primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
     <instance_attributes id="params-public-ip">
        <nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
     </instance_attributes>
    </primitive>
    <primitive id="Email" class="lsb" type="exim"/>
   </resources>
   <constraints>
      <rsc_colocation id="xxx" rsc="Email" with-rsc="Public-IP" score="INFINITY"/>
      <rsc_order id="yyy" first="Public-IP" then="Email"/>
   </constraints>
</configuration>

Obviously as the group grows bigger, the reduced configuration effort can become significant.

Another (typical) example of a group is a DRBD volume, the filesystem mount, an IP address, and an application that uses them.

10.1.1. Group Properties
Properties of a Group Resource
Field Description
id

A unique name for the group

10.1.2. Group Options

Groups inherit the priority, target-role, and is-managed properties from primitive resources. See Resource Options for information about those properties.

Group-specific configuration options
Meta-Attribute Default Description
ordered true

If true, group members will be started in the order they are listed in the configuration (and stopped in the reverse order).

10.1.3. Group Instance Attributes

Groups have no instance attributes. However, any that are set for the group object will be inherited by the group’s children.

10.1.4. Group Contents

Groups may only contain a collection of cluster resources (see Resource Properties). To refer to a child of a group resource, just use the child’s id instead of the group’s.

10.1.5. Group Constraints

Although it is possible to reference a group’s children in constraints, it is usually preferable to reference the group itself.

Some constraints involving groups

<constraints>
    <rsc_location id="group-prefers-node1" rsc="shortcut" node="node1" score="500"/>
    <rsc_colocation id="webserver-with-group" rsc="Webserver" with-rsc="shortcut"/>
    <rsc_order id="start-group-then-webserver" first="Webserver" then="shortcut"/>
</constraints>
10.1.6. Group Stickiness

Stickiness, the measure of how much a resource wants to stay where it is, is additive in groups. Every active resource of the group will contribute its stickiness value to the group’s total. So if the default resource-stickiness is 100, and a group has seven members, five of which are active, then the group as a whole will prefer its current location with a score of 500.

10.2. Clones - Resources That Can Have Multiple Active Instances

Clone resources are resources that can have more than one copy active at the same time. This allows you, for example, to run a copy of a daemon on every node. You can clone any primitive or group resource [1].

10.2.1. Anonymous versus Unique Clones

A clone resource is configured to be either anonymous or globally unique.

Anonymous clones are the simplest. These behave completely identically everywhere they are running. Because of this, there can be only one instance of an anonymous clone active per node.

The instances of globally unique clones are distinct entities. All instances are launched identically, but one instance of the clone is not identical to any other instance, whether running on the same node or a different node. As an example, a cloned IP address can use special kernel functionality such that each instance handles a subset of requests for the same IP address.

10.2.2. Promotable clones

If a clone is promotable, its instances can perform a special role that Pacemaker will manage via the promote and demote actions of the resource agent.

Services that support such a special role have various terms for the special role and the default role: primary and secondary, master and replica, controller and worker, etc. Pacemaker uses the terms promoted and unpromoted to be agnostic to what the service calls them or what they do.

All that Pacemaker cares about is that an instance comes up in the unpromoted role when started, and the resource agent supports the promote and demote actions to manage entering and exiting the promoted role.

10.2.3. Clone Properties
Properties of a Clone Resource
Field Description
id

A unique name for the clone

10.2.4. Clone Options

Options inherited from primitive resources: priority, target-role, is-managed

Clone-specific configuration options
Field Default Description
globally-unique false

If true, each clone instance performs a distinct function

clone-max 0

The maximum number of clone instances that can be started across the entire cluster. If 0, the number of nodes in the cluster will be used.

clone-node-max 1

If globally-unique is true, the maximum number of clone instances that can be started on a single node

clone-min 0

Require at least this number of clone instances to be runnable before allowing resources depending on the clone to be runnable. A value of 0 means require all clone instances to be runnable.

notify false

Call the resource agent’s notify action for all active instances, before and after starting or stopping any clone instance. The resource agent must support this action. Allowed values: false, true

ordered false

If true, clone instances must be started sequentially instead of in parallel. Allowed values: false, true

interleave false

When this clone is ordered relative to another clone, if this option is false (the default), the ordering is relative to all instances of the other clone, whereas if this option is true, the ordering is relative only to instances on the same node. Allowed values: false, true

promotable false

If true, clone instances can perform a special role that Pacemaker will manage via the resource agent’s promote and demote actions. The resource agent must support these actions. Allowed values: false, true

promoted-max 1

If promotable is true, the number of instances that can be promoted at one time across the entire cluster

promoted-node-max 1

If promotable is true and globally-unique is false, the number of clone instances can be promoted at one time on a single node

Note

Deprecated Terminology

In older documentation and online examples, you may see promotable clones referred to as multi-state, stateful, or master/slave; these mean the same thing as promotable. Certain syntax is supported for backward compatibility, but is deprecated and will be removed in a future version:

  • Using a master tag, instead of a clone tag with the promotable meta-attribute set to true
  • Using the master-max meta-attribute instead of promoted-max
  • Using the master-node-max meta-attribute instead of promoted-node-max
  • Using Master as a role name instead of Promoted
  • Using Slave as a role name instead of Unpromoted
10.2.5. Clone Contents

Clones must contain exactly one primitive or group resource.

A clone that runs a web server on all nodes

<clone id="apache-clone">
    <primitive id="apache" class="lsb" type="apache">
        <operations>
           <op id="apache-monitor" name="monitor" interval="30"/>
        </operations>
    </primitive>
</clone>

Warning

You should never reference the name of a clone’s child (the primitive or group resource being cloned). If you think you need to do this, you probably need to re-evaluate your design.

10.2.6. Clone Instance Attribute

Clones have no instance attributes; however, any that are set here will be inherited by the clone’s child.

10.2.7. Clone Constraints

In most cases, a clone will have a single instance on each active cluster node. If this is not the case, you can indicate which nodes the cluster should preferentially assign copies to with resource location constraints. These constraints are written no differently from those for primitive resources except that the clone’s id is used.

Some constraints involving clones

<constraints>
    <rsc_location id="clone-prefers-node1" rsc="apache-clone" node="node1" score="500"/>
    <rsc_colocation id="stats-with-clone" rsc="apache-stats" with="apache-clone"/>
    <rsc_order id="start-clone-then-stats" first="apache-clone" then="apache-stats"/>
</constraints>

Ordering constraints behave slightly differently for clones. In the example above, apache-stats will wait until all copies of apache-clone that need to be started have done so before being started itself. Only if no copies can be started will apache-stats be prevented from being active. Additionally, the clone will wait for apache-stats to be stopped before stopping itself.

Colocation of a primitive or group resource with a clone means that the resource can run on any node with an active instance of the clone. The cluster will choose an instance based on where the clone is running and the resource’s own location preferences.

Colocation between clones is also possible. If one clone A is colocated with another clone B, the set of allowed locations for A is limited to nodes on which B is (or will be) active. Placement is then performed normally.

10.2.7.1. Promotable Clone Constraints

For promotable clone resources, the first-action and/or then-action fields for ordering constraints may be set to promote or demote to constrain the promoted role, and colocation constraints may contain rsc-role and/or with-rsc-role fields.

Constraints involving promotable clone resources

<constraints>
   <rsc_location id="db-prefers-node1" rsc="database" node="node1" score="500"/>
   <rsc_colocation id="backup-with-db-unpromoted" rsc="backup"
     with-rsc="database" with-rsc-role="Unpromoted"/>
   <rsc_colocation id="myapp-with-db-promoted" rsc="myApp"
     with-rsc="database" with-rsc-role="Promoted"/>
   <rsc_order id="start-db-before-backup" first="database" then="backup"/>
   <rsc_order id="promote-db-then-app" first="database" first-action="promote"
     then="myApp" then-action="start"/>
</constraints>

In the example above, myApp will wait until one of the database copies has been started and promoted before being started itself on the same node. Only if no copies can be promoted will myApp be prevented from being active. Additionally, the cluster will wait for myApp to be stopped before demoting the database.

Colocation of a primitive or group resource with a promotable clone resource means that it can run on any node with an active instance of the promotable clone resource that has the specified role (Promoted or Unpromoted). In the example above, the cluster will choose a location based on where database is running in the promoted role, and if there are multiple promoted instances it will also factor in myApp’s own location preferences when deciding which location to choose.

Colocation with regular clones and other promotable clone resources is also possible. In such cases, the set of allowed locations for the rsc clone is (after role filtering) limited to nodes on which the with-rsc promotable clone resource is (or will be) in the specified role. Placement is then performed as normal.

10.2.7.2. Using Promotable Clone Resources in Colocation Sets

When a promotable clone is used in a resource set inside a colocation constraint, the resource set may take a role attribute.

In the following example, an instance of B may be promoted only on a node where A is in the promoted role. Additionally, resources C and D must be located on a node where both A and B are promoted.

Colocate C and D with A’s and B’s promoted instances

<constraints>
    <rsc_colocation id="coloc-1" score="INFINITY" >
      <resource_set id="colocated-set-example-1" sequential="true" role="Promoted">
        <resource_ref id="A"/>
        <resource_ref id="B"/>
      </resource_set>
      <resource_set id="colocated-set-example-2" sequential="true">
        <resource_ref id="C"/>
        <resource_ref id="D"/>
      </resource_set>
    </rsc_colocation>
</constraints>
10.2.7.3. Using Promotable Clone Resources in Ordered Sets

When a promotable clone is used in a resource set inside an ordering constraint, the resource set may take an action attribute.

Start C and D after first promoting A and B

<constraints>
    <rsc_order id="order-1" score="INFINITY" >
      <resource_set id="ordered-set-1" sequential="true" action="promote">
        <resource_ref id="A"/>
        <resource_ref id="B"/>
      </resource_set>
      <resource_set id="ordered-set-2" sequential="true" action="start">
        <resource_ref id="C"/>
        <resource_ref id="D"/>
      </resource_set>
    </rsc_order>
</constraints>

In the above example, B cannot be promoted until A has been promoted. Additionally, resources C and D must wait until A and B have been promoted before they can start.

10.2.8. Clone Stickiness

To achieve a stable allocation pattern, clones are slightly sticky by default. If no value for resource-stickiness is provided, the clone will use a value of 1. Being a small value, it causes minimal disturbance to the score calculations of other resources but is enough to prevent Pacemaker from needlessly moving copies around the cluster.

Note

For globally unique clones, this may result in multiple instances of the clone staying on a single node, even after another eligible node becomes active (for example, after being put into standby mode then made active again). If you do not want this behavior, specify a resource-stickiness of 0 for the clone temporarily and let the cluster adjust, then set it back to 1 if you want the default behavior to apply again.

Important

If resource-stickiness is set in the rsc_defaults section, it will apply to clone instances as well. This means an explicit resource-stickiness of 0 in rsc_defaults works differently from the implicit default used when resource-stickiness is not specified.

10.2.9. Clone Resource Agent Requirements

Any resource can be used as an anonymous clone, as it requires no additional support from the resource agent. Whether it makes sense to do so depends on your resource and its resource agent.

10.2.9.1. Resource Agent Requirements for Globally Unique Clones

Globally unique clones require additional support in the resource agent. In particular, it must only respond with ${OCF_SUCCESS} if the node has that exact instance active. All other probes for instances of the clone should result in ${OCF_NOT_RUNNING} (or one of the other OCF error codes if they are failed).

Individual instances of a clone are identified by appending a colon and a numerical offset, e.g. apache:2.

Resource agents can find out how many copies there are by examining the OCF_RESKEY_CRM_meta_clone_max environment variable and which instance it is by examining OCF_RESKEY_CRM_meta_clone.

The resource agent must not make any assumptions (based on OCF_RESKEY_CRM_meta_clone) about which numerical instances are active. In particular, the list of active copies will not always be an unbroken sequence, nor always start at 0.

10.2.9.2. Resource Agent Requirements for Promotable Clones

Promotable clone resources require two extra actions, demote and promote, which are responsible for changing the state of the resource. Like start and stop, they should return ${OCF_SUCCESS} if they completed successfully or a relevant error code if they did not.

The states can mean whatever you wish, but when the resource is started, it must come up in the unpromoted role. From there, the cluster will decide which instances to promote.

In addition to the clone requirements for monitor actions, agents must also accurately report which state they are in. The cluster relies on the agent to report its status (including role) accurately and does not indicate to the agent what role it currently believes it to be in.

Role implications of OCF return codes
Monitor Return Code Description
OCF_NOT_RUNNING

Stopped

OCF_SUCCESS

Running (Unpromoted)

OCF_RUNNING_PROMOTED

Running (Promoted)

OCF_FAILED_PROMOTED

Failed (Promoted)

Other

Failed (Unpromoted)

10.2.9.3. Clone Notifications

If the clone has the notify meta-attribute set to true, and the resource agent supports the notify action, Pacemaker will call the action when appropriate, passing a number of extra variables which, when combined with additional context, can be used to calculate the current state of the cluster and what is about to happen to it.

Environment variables supplied with Clone notify actions
Variable Description
OCF_RESKEY_CRM_meta_notify_type

Allowed values: pre, post

OCF_RESKEY_CRM_meta_notify_operation

Allowed values: start, stop

OCF_RESKEY_CRM_meta_notify_start_resource

Resources to be started

OCF_RESKEY_CRM_meta_notify_stop_resource

Resources to be stopped

OCF_RESKEY_CRM_meta_notify_active_resource

Resources that are running

OCF_RESKEY_CRM_meta_notify_inactive_resource

Resources that are not running

OCF_RESKEY_CRM_meta_notify_start_uname

Nodes on which resources will be started

OCF_RESKEY_CRM_meta_notify_stop_uname

Nodes on which resources will be stopped

OCF_RESKEY_CRM_meta_notify_active_uname

Nodes on which resources are running

The variables come in pairs, such as OCF_RESKEY_CRM_meta_notify_start_resource and OCF_RESKEY_CRM_meta_notify_start_uname, and should be treated as an array of whitespace-separated elements.

OCF_RESKEY_CRM_meta_notify_inactive_resource is an exception, as the matching uname variable does not exist since inactive resources are not running on any node.

Thus, in order to indicate that clone:0 will be started on sles-1, clone:2 will be started on sles-3, and clone:3 will be started on sles-2, the cluster would set:

Notification variables

OCF_RESKEY_CRM_meta_notify_start_resource="clone:0 clone:2 clone:3"
OCF_RESKEY_CRM_meta_notify_start_uname="sles-1 sles-3 sles-2"

Note

Pacemaker will log but otherwise ignore failures of notify actions.

10.2.9.4. Interpretation of Notification Variables

Pre-notification (stop):

  • Active resources: $OCF_RESKEY_CRM_meta_notify_active_resource
  • Inactive resources: $OCF_RESKEY_CRM_meta_notify_inactive_resource
  • Resources to be started: $OCF_RESKEY_CRM_meta_notify_start_resource
  • Resources to be stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

Post-notification (stop) / Pre-notification (start):

  • Active resources

    • $OCF_RESKEY_CRM_meta_notify_active_resource
    • minus $OCF_RESKEY_CRM_meta_notify_stop_resource
  • Inactive resources

    • $OCF_RESKEY_CRM_meta_notify_inactive_resource
    • plus $OCF_RESKEY_CRM_meta_notify_stop_resource
  • Resources that were started: $OCF_RESKEY_CRM_meta_notify_start_resource

  • Resources that were stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

Post-notification (start):

  • Active resources:

    • $OCF_RESKEY_CRM_meta_notify_active_resource
    • minus $OCF_RESKEY_CRM_meta_notify_stop_resource
    • plus $OCF_RESKEY_CRM_meta_notify_start_resource
  • Inactive resources:

    • $OCF_RESKEY_CRM_meta_notify_inactive_resource
    • plus $OCF_RESKEY_CRM_meta_notify_stop_resource
    • minus $OCF_RESKEY_CRM_meta_notify_start_resource
  • Resources that were started: $OCF_RESKEY_CRM_meta_notify_start_resource

  • Resources that were stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

10.2.9.5. Extra Notifications for Promotable Clones
Extra environment variables supplied for promotable clones
Variable Description
OCF_RESKEY_CRM_meta_notify_promoted_resource

Resources that are running in the promoted role

OCF_RESKEY_CRM_meta_notify_unpromoted_resource

Resources that are running in the unpromoted role

OCF_RESKEY_CRM_meta_notify_promote_resource

Resources to be promoted

OCF_RESKEY_CRM_meta_notify_demote_resource

Resources to be demoted

OCF_RESKEY_CRM_meta_notify_promote_uname

Nodes on which resources will be promoted

OCF_RESKEY_CRM_meta_notify_demote_uname

Nodes on which resources will be demoted

OCF_RESKEY_CRM_meta_notify_promoted_uname

Nodes on which resources are running in the promoted role

OCF_RESKEY_CRM_meta_notify_unpromoted_uname

Nodes on which resources are running in the unpromoted role

10.2.9.6. Interpretation of Promotable Notification Variables

Pre-notification (demote):

  • Active resources: $OCF_RESKEY_CRM_meta_notify_active_resource
  • Promoted resources: $OCF_RESKEY_CRM_meta_notify_promoted_resource
  • Unpromoted resources: $OCF_RESKEY_CRM_meta_notify_unpromoted_resource
  • Inactive resources: $OCF_RESKEY_CRM_meta_notify_inactive_resource
  • Resources to be started: $OCF_RESKEY_CRM_meta_notify_start_resource
  • Resources to be promoted: $OCF_RESKEY_CRM_meta_notify_promote_resource
  • Resources to be demoted: $OCF_RESKEY_CRM_meta_notify_demote_resource
  • Resources to be stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

Post-notification (demote) / Pre-notification (stop):

  • Active resources: $OCF_RESKEY_CRM_meta_notify_active_resource

  • Promoted resources:

    • $OCF_RESKEY_CRM_meta_notify_promoted_resource
    • minus $OCF_RESKEY_CRM_meta_notify_demote_resource
  • Unpromoted resources: $OCF_RESKEY_CRM_meta_notify_unpromoted_resource

  • Inactive resources: $OCF_RESKEY_CRM_meta_notify_inactive_resource

  • Resources to be started: $OCF_RESKEY_CRM_meta_notify_start_resource

  • Resources to be promoted: $OCF_RESKEY_CRM_meta_notify_promote_resource

  • Resources to be demoted: $OCF_RESKEY_CRM_meta_notify_demote_resource

  • Resources to be stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

  • Resources that were demoted: $OCF_RESKEY_CRM_meta_notify_demote_resource

Post-notification (stop) / Pre-notification (start)

  • Active resources:

    • $OCF_RESKEY_CRM_meta_notify_active_resource
    • minus $OCF_RESKEY_CRM_meta_notify_stop_resource
  • Promoted resources:

    • $OCF_RESKEY_CRM_meta_notify_promoted_resource
    • minus $OCF_RESKEY_CRM_meta_notify_demote_resource
  • Unpromoted resources:

    • $OCF_RESKEY_CRM_meta_notify_unpromoted_resource
    • minus $OCF_RESKEY_CRM_meta_notify_stop_resource
  • Inactive resources:

    • $OCF_RESKEY_CRM_meta_notify_inactive_resource
    • plus $OCF_RESKEY_CRM_meta_notify_stop_resource
  • Resources to be started: $OCF_RESKEY_CRM_meta_notify_start_resource

  • Resources to be promoted: $OCF_RESKEY_CRM_meta_notify_promote_resource

  • Resources to be demoted: $OCF_RESKEY_CRM_meta_notify_demote_resource

  • Resources to be stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

  • Resources that were demoted: $OCF_RESKEY_CRM_meta_notify_demote_resource

  • Resources that were stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

Post-notification (start) / Pre-notification (promote)

  • Active resources:

    • $OCF_RESKEY_CRM_meta_notify_active_resource
    • minus $OCF_RESKEY_CRM_meta_notify_stop_resource
    • plus $OCF_RESKEY_CRM_meta_notify_start_resource
  • Promoted resources:

    • $OCF_RESKEY_CRM_meta_notify_promoted_resource
    • minus $OCF_RESKEY_CRM_meta_notify_demote_resource
  • Unpromoted resources:

    • $OCF_RESKEY_CRM_meta_notify_unpromoted_resource
    • minus $OCF_RESKEY_CRM_meta_notify_stop_resource
    • plus $OCF_RESKEY_CRM_meta_notify_start_resource
  • Inactive resources:

    • $OCF_RESKEY_CRM_meta_notify_inactive_resource
    • plus $OCF_RESKEY_CRM_meta_notify_stop_resource
    • minus $OCF_RESKEY_CRM_meta_notify_start_resource
  • Resources to be started: $OCF_RESKEY_CRM_meta_notify_start_resource

  • Resources to be promoted: $OCF_RESKEY_CRM_meta_notify_promote_resource

  • Resources to be demoted: $OCF_RESKEY_CRM_meta_notify_demote_resource

  • Resources to be stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

  • Resources that were started: $OCF_RESKEY_CRM_meta_notify_start_resource

  • Resources that were demoted: $OCF_RESKEY_CRM_meta_notify_demote_resource

  • Resources that were stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

Post-notification (promote)

  • Active resources:

    • $OCF_RESKEY_CRM_meta_notify_active_resource
    • minus $OCF_RESKEY_CRM_meta_notify_stop_resource
    • plus $OCF_RESKEY_CRM_meta_notify_start_resource
  • Promoted resources:

    • $OCF_RESKEY_CRM_meta_notify_promoted_resource
    • minus $OCF_RESKEY_CRM_meta_notify_demote_resource
    • plus $OCF_RESKEY_CRM_meta_notify_promote_resource
  • Unpromoted resources:

    • $OCF_RESKEY_CRM_meta_notify_unpromoted_resource
    • minus $OCF_RESKEY_CRM_meta_notify_stop_resource
    • plus $OCF_RESKEY_CRM_meta_notify_start_resource
    • minus $OCF_RESKEY_CRM_meta_notify_promote_resource
  • Inactive resources:

    • $OCF_RESKEY_CRM_meta_notify_inactive_resource
    • plus $OCF_RESKEY_CRM_meta_notify_stop_resource
    • minus $OCF_RESKEY_CRM_meta_notify_start_resource
  • Resources to be started: $OCF_RESKEY_CRM_meta_notify_start_resource

  • Resources to be promoted: $OCF_RESKEY_CRM_meta_notify_promote_resource

  • Resources to be demoted: $OCF_RESKEY_CRM_meta_notify_demote_resource

  • Resources to be stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

  • Resources that were started: $OCF_RESKEY_CRM_meta_notify_start_resource

  • Resources that were promoted: $OCF_RESKEY_CRM_meta_notify_promote_resource

  • Resources that were demoted: $OCF_RESKEY_CRM_meta_notify_demote_resource

  • Resources that were stopped: $OCF_RESKEY_CRM_meta_notify_stop_resource

10.2.10. Monitoring Promotable Clone Resources

The usual monitor actions are insufficient to monitor a promotable clone resource, because Pacemaker needs to verify not only that the resource is active, but also that its actual role matches its intended one.

Define two monitoring actions: the usual one will cover the unpromoted role, and an additional one with role="Promoted" will cover the promoted role.

Monitoring both states of a promotable clone resource

<clone id="myPromotableRsc">
   <meta_attributes id="myPromotableRsc-meta">
       <nvpair name="promotable" value="true"/>
   </meta_attributes>
   <primitive id="myRsc" class="ocf" type="myApp" provider="myCorp">
    <operations>
     <op id="public-ip-unpromoted-check" name="monitor" interval="60"/>
     <op id="public-ip-promoted-check" name="monitor" interval="61" role="Promoted"/>
    </operations>
   </primitive>
</clone>

Important

It is crucial that every monitor operation has a different interval! Pacemaker currently differentiates between operations only by resource and interval; so if (for example) a promotable clone resource had the same monitor interval for both roles, Pacemaker would ignore the role when checking the status – which would cause unexpected return codes, and therefore unnecessary complications.

10.2.11. Determining Which Instance is Promoted

Pacemaker can choose a promotable clone instance to be promoted in one of two ways:

  • Promotion scores: These are node attributes set via the crm_attribute command using the --promotion option, which generally would be called by the resource agent’s start action if it supports promotable clones. This tool automatically detects both the resource and host, and should be used to set a preference for being promoted. Based on this, promoted-max, and promoted-node-max, the instance(s) with the highest preference will be promoted.
  • Constraints: Location constraints can indicate which nodes are most preferred to be promoted.

Explicitly preferring node1 to be promoted

<rsc_location id="promoted-location" rsc="myPromotableRsc">
    <rule id="promoted-rule" score="100" role="Promoted">
      <expression id="promoted-exp" attribute="#uname" operation="eq" value="node1"/>
    </rule>
</rsc_location>

10.3. Bundles - Containerized Resources

Pacemaker supports a special syntax for launching a service inside a container with any infrastructure it requires: the bundle.

Pacemaker bundles support Docker, podman (since 2.0.1), and rkt container technologies. [2]

A bundle for a containerized web server

<bundle id="httpd-bundle">
   <podman image="pcmk:http" replicas="3"/>
   <network ip-range-start="192.168.122.131"
            host-netmask="24"
            host-interface="eth0">
      <port-mapping id="httpd-port" port="80"/>
      </network>
   <storage>
      <storage-mapping id="httpd-syslog"
                       source-dir="/dev/log"
                       target-dir="/dev/log"
                       options="rw"/>
      <storage-mapping id="httpd-root"
                       source-dir="/srv/html"
                       target-dir="/var/www/html"
                       options="rw,Z"/>
      <storage-mapping id="httpd-logs"
                       source-dir-root="/var/log/pacemaker/bundles"
                       target-dir="/etc/httpd/logs"
                       options="rw,Z"/>
   </storage>
   <primitive class="ocf" id="httpd" provider="heartbeat" type="apache"/>
</bundle>
10.3.1. Bundle Prerequisites

Before configuring a bundle in Pacemaker, the user must install the appropriate container launch technology (Docker, podman, or rkt), and supply a fully configured container image, on every node allowed to run the bundle.

Pacemaker will create an implicit resource of type ocf:heartbeat:docker, ocf:heartbeat:podman, or ocf:heartbeat:rkt to manage a bundle’s container. The user must ensure that the appropriate resource agent is installed on every node allowed to run the bundle.

10.3.2. Bundle Properties
XML Attributes of a bundle Element
Attribute Description
id

A unique name for the bundle (required)

description

Arbitrary text (not used by Pacemaker)

A bundle must contain exactly one docker, podman, or rkt element.

10.3.3. Bundle Container Properties
XML attributes of a docker, podman, or rkt Element
Attribute Default Description
image  

Container image tag (required)

replicas Value of promoted-max if that is positive, else 1

A positive integer specifying the number of container instances to launch

replicas-per-host 1

A positive integer specifying the number of container instances allowed to run on a single node

promoted-max 0

A non-negative integer that, if positive, indicates that the containerized service should be treated as a promotable service, with this many replicas allowed to run the service in the promoted role

network  

If specified, this will be passed to the docker run, podman run, or rkt run command as the network setting for the container.

run-command /usr/sbin/pacemaker-remoted if bundle contains a primitive, otherwise none

This command will be run inside the container when launching it (“PID 1”). If the bundle contains a primitive, this command must start pacemaker-remoted (but could, for example, be a script that does other stuff, too).

options  

Extra command-line options to pass to the docker run, podman run, or rkt run command

Note

Considerations when using cluster configurations or container images from Pacemaker 1.1:

  • If the container image has a pre-2.0.0 version of Pacemaker, set run-command to /usr/sbin/pacemaker_remoted (note the underbar instead of dash).
  • masters is accepted as an alias for promoted-max, but is deprecated since 2.0.0, and support for it will be removed in a future version.
10.3.4. Bundle Network Properties

A bundle may optionally contain one <network> element.

XML attributes of a network Element

Attribute Default Description
add-host TRUE

If TRUE, and ip-range-start is used, Pacemaker will automatically ensure that /etc/hosts inside the containers has entries for each replica name and its assigned IP.

ip-range-start  

If specified, Pacemaker will create an implicit ocf:heartbeat:IPaddr2 resource for each container instance, starting with this IP address, using up to replicas sequential addresses. These addresses can be used from the host’s network to reach the service inside the container, though it is not visible within the container itself. Only IPv4 addresses are currently supported.

host-netmask 32

If ip-range-start is specified, the IP addresses are created with this CIDR netmask (as a number of bits).

host-interface  

If ip-range-start is specified, the IP addresses are created on this host interface (by default, it will be determined from the IP address).

control-port 3121

If the bundle contains a primitive, the cluster will use this integer TCP port for communication with Pacemaker Remote inside the container. Changing this is useful when the container is unable to listen on the default port, for example, when the container uses the host’s network rather than ip-range-start (in which case replicas-per-host must be 1), or when the bundle may run on a Pacemaker Remote node that is already listening on the default port. Any PCMK_remote_port environment variable set on the host or in the container is ignored for bundle connections.

Note

Replicas are named by the bundle id plus a dash and an integer counter starting with zero. For example, if a bundle named httpd-bundle has replicas=2, its containers will be named httpd-bundle-0 and httpd-bundle-1.

Additionally, a network element may optionally contain one or more port-mapping elements.

Attributes of a port-mapping Element
Attribute Default Description
id  

A unique name for the port mapping (required)

port  

If this is specified, connections to this TCP port number on the host network (on the container’s assigned IP address, if ip-range-start is specified) will be forwarded to the container network. Exactly one of port or range must be specified in a port-mapping.

internal-port value of port

If port and this are specified, connections to port on the host’s network will be forwarded to this port on the container network.

range  

If this is specified, connections to these TCP port numbers (expressed as first_port-last_port) on the host network (on the container’s assigned IP address, if ip-range-start is specified) will be forwarded to the same ports in the container network. Exactly one of port or range must be specified in a port-mapping.

Note

If the bundle contains a primitive, Pacemaker will automatically map the control-port, so it is not necessary to specify that port in a port-mapping.

10.3.5. Bundle Storage Properties

A bundle may optionally contain one storage element. A storage element has no properties of its own, but may contain one or more storage-mapping elements.

Attributes of a storage-mapping Element
Attribute Default Description
id  

A unique name for the storage mapping (required)

source-dir  

The absolute path on the host’s filesystem that will be mapped into the container. Exactly one of source-dir and source-dir-root must be specified in a storage-mapping.

source-dir-root  

The start of a path on the host’s filesystem that will be mapped into the container, using a different subdirectory on the host for each container instance. The subdirectory will be named the same as the replica name. Exactly one of source-dir and source-dir-root must be specified in a storage-mapping.

target-dir  

The path name within the container where the host storage will be mapped (required)

options  

A comma-separated list of file system mount options to use when mapping the storage

Note

Pacemaker does not define the behavior if the source directory does not already exist on the host. However, it is expected that the container technology and/or its resource agent will create the source directory in that case.

Note

If the bundle contains a primitive, Pacemaker will automatically map the equivalent of source-dir=/etc/pacemaker/authkey target-dir=/etc/pacemaker/authkey and source-dir-root=/var/log/pacemaker/bundles target-dir=/var/log into the container, so it is not necessary to specify those paths in a storage-mapping.

Important

The PCMK_authkey_location environment variable must not be set to anything other than the default of /etc/pacemaker/authkey on any node in the cluster.

Important

If SELinux is used in enforcing mode on the host, you must ensure the container is allowed to use any storage you mount into it. For Docker and podman bundles, adding “Z” to the mount options will create a container-specific label for the mount that allows the container access.

10.3.6. Bundle Primitive

A bundle may optionally contain one primitive resource. The primitive may have operations, instance attributes, and meta-attributes defined, as usual.

If a bundle contains a primitive resource, the container image must include the Pacemaker Remote daemon, and at least one of ip-range-start or control-port must be configured in the bundle. Pacemaker will create an implicit ocf:pacemaker:remote resource for the connection, launch Pacemaker Remote within the container, and monitor and manage the primitive resource via Pacemaker Remote.

If the bundle has more than one container instance (replica), the primitive resource will function as an implicit clone – a promotable clone if the bundle has promoted-max greater than zero.

Note

If you want to pass environment variables to a bundle’s Pacemaker Remote connection or primitive, you have two options:

  • Environment variables whose value is the same regardless of the underlying host may be set using the container element’s options attribute.
  • If you want variables to have host-specific values, you can use the storage-mapping element to map a file on the host as /etc/pacemaker/pcmk-init.env in the container (since 2.0.3). Pacemaker Remote will parse this file as a shell-like format, with variables set as NAME=VALUE, ignoring blank lines and comments starting with “#”.

Important

When a bundle has a primitive, Pacemaker on all cluster nodes must be able to contact Pacemaker Remote inside the bundle’s containers.

  • The containers must have an accessible network (for example, network should not be set to “none” with a primitive).
  • The default, using a distinct network space inside the container, works in combination with ip-range-start. Any firewall must allow access from all cluster nodes to the control-port on the container IPs.
  • If the container shares the host’s network space (for example, by setting network to “host”), a unique control-port should be specified for each bundle. Any firewall must allow access from all cluster nodes to the control-port on all cluster and remote node IPs.
10.3.7. Bundle Node Attributes

If the bundle has a primitive, the primitive’s resource agent may want to set node attributes such as promotion scores. However, with containers, it is not apparent which node should get the attribute.

If the container uses shared storage that is the same no matter which node the container is hosted on, then it is appropriate to use the promotion score on the bundle node itself.

On the other hand, if the container uses storage exported from the underlying host, then it may be more appropriate to use the promotion score on the underlying host.

Since this depends on the particular situation, the container-attribute-target resource meta-attribute allows the user to specify which approach to use. If it is set to host, then user-defined node attributes will be checked on the underlying host. If it is anything else, the local node (in this case the bundle node) is used as usual.

This only applies to user-defined attributes; the cluster will always check the local node for cluster-defined attributes such as #uname.

If container-attribute-target is host, the cluster will pass additional environment variables to the primitive’s resource agent that allow it to set node attributes appropriately: CRM_meta_container_attribute_target (identical to the meta-attribute value) and CRM_meta_physical_host (the name of the underlying host).

Note

When called by a resource agent, the attrd_updater and crm_attribute commands will automatically check those environment variables and set attributes appropriately.

10.3.8. Bundle Meta-Attributes

Any meta-attribute set on a bundle will be inherited by the bundle’s primitive and any resources implicitly created by Pacemaker for the bundle.

This includes options such as priority, target-role, and is-managed. See Resource Options for more information.

10.3.9. Limitations of Bundles

Restarting pacemaker while a bundle is unmanaged or the cluster is in maintenance mode may cause the bundle to fail.

Bundles may not be explicitly cloned or included in groups. This includes the bundle’s primitive and any resources implicitly created by Pacemaker for the bundle. (If replicas is greater than 1, the bundle will behave like a clone implicitly.)

Bundles do not have instance attributes, utilization attributes, or operations, though a bundle’s primitive may have them.

A bundle with a primitive can run on a Pacemaker Remote node only if the bundle uses a distinct control-port.

[1]Of course, the service must support running multiple instances.
[2]Docker is a trademark of Docker, Inc. No endorsement by or association with Docker, Inc. is implied.

11. Reusing Parts of the Configuration

Pacemaker provides multiple ways to simplify the configuration XML by reusing parts of it in multiple places.

Besides simplifying the XML, this also allows you to manipulate multiple configuration elements with a single reference.

11.1. Reusing Resource Definitions

If you want to create lots of resources with similar configurations, defining a resource template simplifies the task. Once defined, it can be referenced in primitives or in certain types of constraints.

11.1.1. Configuring Resources with Templates

The primitives referencing the template will inherit all meta-attributes, instance attributes, utilization attributes and operations defined in the template. And you can define specific attributes and operations for any of the primitives. If any of these are defined in both the template and the primitive, the values defined in the primitive will take precedence over the ones defined in the template.

Hence, resource templates help to reduce the amount of configuration work. If any changes are needed, they can be done to the template definition and will take effect globally in all resource definitions referencing that template.

Resource templates have a syntax similar to that of primitives.

Resource template for a migratable Xen virtual machine

<template id="vm-template" class="ocf" provider="heartbeat" type="Xen">
  <meta_attributes id="vm-template-meta_attributes">
    <nvpair id="vm-template-meta_attributes-allow-migrate" name="allow-migrate" value="true"/>
  </meta_attributes>
  <utilization id="vm-template-utilization">
    <nvpair id="vm-template-utilization-memory" name="memory" value="512"/>
  </utilization>
  <operations>
    <op id="vm-template-monitor-15s" interval="15s" name="monitor" timeout="60s"/>
    <op id="vm-template-start-0" interval="0" name="start" timeout="60s"/>
  </operations>
</template>

Once you define a resource template, you can use it in primitives by specifying the template property.

Xen primitive resource using a resource template

<primitive id="vm1" template="vm-template">
  <instance_attributes id="vm1-instance_attributes">
    <nvpair id="vm1-instance_attributes-name" name="name" value="vm1"/>
    <nvpair id="vm1-instance_attributes-xmfile" name="xmfile" value="/etc/xen/shared-vm/vm1"/>
  </instance_attributes>
</primitive>

In the example above, the new primitive vm1 will inherit everything from vm-template. For example, the equivalent of the above two examples would be:

Equivalent Xen primitive resource not using a resource template

<primitive id="vm1" class="ocf" provider="heartbeat" type="Xen">
  <meta_attributes id="vm-template-meta_attributes">
    <nvpair id="vm-template-meta_attributes-allow-migrate" name="allow-migrate" value="true"/>
  </meta_attributes>
  <utilization id="vm-template-utilization">
    <nvpair id="vm-template-utilization-memory" name="memory" value="512"/>
  </utilization>
  <operations>
    <op id="vm-template-monitor-15s" interval="15s" name="monitor" timeout="60s"/>
    <op id="vm-template-start-0" interval="0" name="start" timeout="60s"/>
  </operations>
  <instance_attributes id="vm1-instance_attributes">
    <nvpair id="vm1-instance_attributes-name" name="name" value="vm1"/>
    <nvpair id="vm1-instance_attributes-xmfile" name="xmfile" value="/etc/xen/shared-vm/vm1"/>
  </instance_attributes>
</primitive>

If you want to overwrite some attributes or operations, add them to the particular primitive’s definition.

Xen resource overriding template values

<primitive id="vm2" template="vm-template">
  <meta_attributes id="vm2-meta_attributes">
    <nvpair id="vm2-meta_attributes-allow-migrate" name="allow-migrate" value="false"/>
  </meta_attributes>
  <utilization id="vm2-utilization">
    <nvpair id="vm2-utilization-memory" name="memory" value="1024"/>
  </utilization>
  <instance_attributes id="vm2-instance_attributes">
    <nvpair id="vm2-instance_attributes-name" name="name" value="vm2"/>
    <nvpair id="vm2-instance_attributes-xmfile" name="xmfile" value="/etc/xen/shared-vm/vm2"/>
  </instance_attributes>
  <operations>
    <op id="vm2-monitor-30s" interval="30s" name="monitor" timeout="120s"/>
    <op id="vm2-stop-0" interval="0" name="stop" timeout="60s"/>
  </operations>
</primitive>

In the example above, the new primitive vm2 has special attribute values. Its monitor operation has a longer timeout and interval, and the primitive has an additional stop operation.

To see the resulting definition of a resource, run:

# crm_resource --query-xml --resource vm2

To see the raw definition of a resource in the CIB, run:

# crm_resource --query-xml-raw --resource vm2
11.1.2. Using Templates in Constraints

A resource template can be referenced in the following types of constraints:

Resource templates referenced in constraints stand for all primitives which are derived from that template. This means, the constraint applies to all primitive resources referencing the resource template. Referencing resource templates in constraints is an alternative to resource sets and can simplify the cluster configuration considerably.

For example, given the example templates earlier in this chapter:

<rsc_colocation id="vm-template-colo-base-rsc" rsc="vm-template" rsc-role="Started" with-rsc="base-rsc" score="INFINITY"/>

would colocate all VMs with base-rsc and is the equivalent of the following constraint configuration:

<rsc_colocation id="vm-colo-base-rsc" score="INFINITY">
  <resource_set id="vm-colo-base-rsc-0" sequential="false" role="Started">
    <resource_ref id="vm1"/>
    <resource_ref id="vm2"/>
  </resource_set>
  <resource_set id="vm-colo-base-rsc-1">
    <resource_ref id="base-rsc"/>
  </resource_set>
</rsc_colocation>

Note

In a colocation constraint, only one template may be referenced from either rsc or with-rsc; the other reference must be a regular resource.

11.1.3. Using Templates in Resource Sets

Resource templates can also be referenced in resource sets.

For example, given the example templates earlier in this section, then:

<rsc_order id="order1" score="INFINITY">
  <resource_set id="order1-0">
    <resource_ref id="base-rsc"/>
    <resource_ref id="vm-template"/>
    <resource_ref id="top-rsc"/>
  </resource_set>
</rsc_order>

is the equivalent of the following constraint using a sequential resource set:

<rsc_order id="order1" score="INFINITY">
  <resource_set id="order1-0">
    <resource_ref id="base-rsc"/>
    <resource_ref id="vm1"/>
    <resource_ref id="vm2"/>
    <resource_ref id="top-rsc"/>
  </resource_set>
</rsc_order>

Or, if the resources referencing the template can run in parallel, then:

<rsc_order id="order2" score="INFINITY">
  <resource_set id="order2-0">
    <resource_ref id="base-rsc"/>
  </resource_set>
  <resource_set id="order2-1" sequential="false">
    <resource_ref id="vm-template"/>
  </resource_set>
  <resource_set id="order2-2">
    <resource_ref id="top-rsc"/>
  </resource_set>
</rsc_order>

is the equivalent of the following constraint configuration:

<rsc_order id="order2" score="INFINITY">
  <resource_set id="order2-0">
    <resource_ref id="base-rsc"/>
  </resource_set>
  <resource_set id="order2-1" sequential="false">
    <resource_ref id="vm1"/>
    <resource_ref id="vm2"/>
  </resource_set>
  <resource_set id="order2-2">
    <resource_ref id="top-rsc"/>
  </resource_set>
</rsc_order>

11.2. Reusing Rules, Options and Sets of Operations

Sometimes a number of constraints need to use the same set of rules, and resources need to set the same options and parameters. To simplify this situation, you can refer to an existing object using an id-ref instead of an id.

So if for one resource you have

<rsc_location id="WebServer-connectivity" rsc="Webserver">
   <rule id="ping-prefer-rule" score-attribute="pingd" >
    <expression id="ping-prefer" attribute="pingd" operation="defined"/>
   </rule>
</rsc_location>

Then instead of duplicating the rule for all your other resources, you can instead specify:

Referencing rules from other constraints

<rsc_location id="WebDB-connectivity" rsc="WebDB">
   <rule id-ref="ping-prefer-rule"/>
</rsc_location>

Important

The cluster will insist that the rule exists somewhere. Attempting to add a reference to a non-existing rule will cause a validation failure, as will attempting to remove a rule that is referenced elsewhere.

The same principle applies for meta_attributes and instance_attributes as illustrated in the example below:

Referencing attributes, options, and operations from other resources

<primitive id="mySpecialRsc" class="ocf" type="Special" provider="me">
   <instance_attributes id="mySpecialRsc-attrs" score="1" >
     <nvpair id="default-interface" name="interface" value="eth0"/>
     <nvpair id="default-port" name="port" value="9999"/>
   </instance_attributes>
   <meta_attributes id="mySpecialRsc-options">
     <nvpair id="failure-timeout" name="failure-timeout" value="5m"/>
     <nvpair id="migration-threshold" name="migration-threshold" value="1"/>
     <nvpair id="stickiness" name="resource-stickiness" value="0"/>
   </meta_attributes>
   <operations id="health-checks">
     <op id="health-check" name="monitor" interval="60s"/>
     <op id="health-check" name="monitor" interval="30min"/>
   </operations>
</primitive>
<primitive id="myOtherlRsc" class="ocf" type="Other" provider="me">
   <instance_attributes id-ref="mySpecialRsc-attrs"/>
   <meta_attributes id-ref="mySpecialRsc-options"/>
   <operations id-ref="health-checks"/>
</primitive>

id-ref can similarly be used with resource_set (in any constraint type), nvpair, and operations.

11.3. Tagging Configuration Elements

Pacemaker allows you to tag any configuration element that has an XML ID.

The main purpose of tagging is to support higher-level user interface tools; Pacemaker itself only uses tags within constraints. Therefore, what you can do with tags mostly depends on the tools you use.

11.3.1. Configuring Tags

A tag is simply a named list of XML IDs.

Tag referencing three resources

<tags>
  <tag id="all-vms">
    <obj_ref id="vm1"/>
    <obj_ref id="vm2"/>
    <obj_ref id="vm3"/>
  </tag>
</tags>

What you can do with this new tag depends on what your higher-level tools support. For example, a tool might allow you to enable or disable all of the tagged resources at once, or show the status of just the tagged resources.

A single configuration element can be listed in any number of tags.

11.3.2. Using Tags in Constraints and Resource Sets

Pacemaker itself only uses tags in constraints. If you supply a tag name instead of a resource name in any constraint, the constraint will apply to all resources listed in that tag.

Constraint using a tag

<rsc_order id="order1" first="storage" then="all-vms" kind="Mandatory" />

In the example above, assuming the all-vms tag is defined as in the previous example, the constraint will behave the same as:

Equivalent constraints without tags

<rsc_order id="order1-1" first="storage" then="vm1" kind="Mandatory" />
<rsc_order id="order1-2" first="storage" then="vm2" kind="Mandatory" />
<rsc_order id="order1-3" first="storage" then="vm3" kind="Mandatory" />

A tag may be used directly in the constraint, or indirectly by being listed in a resource set used in the constraint. When used in a resource set, an expanded tag will honor the set’s sequential property.

11.3.3. Filtering With Tags

The crm_mon tool can be used to display lots of information about the state of the cluster. On large or complicated clusters, this can include a lot of information, which makes it difficult to find the one thing you are interested in. The --resource= and --node= command line options can be used to filter results. In their most basic usage, these options take a single resource or node name. However, they can also be supplied with a tag name to display several objects at once.

For instance, given the following CIB section:

<resources>
  <primitive class="stonith" id="Fencing" type="fence_xvm"/>
  <primitive class="ocf" id="dummy" provider="pacemaker" type="Dummy"/>
  <group id="inactive-group">
    <primitive class="ocf" id="inactive-dummy-1" provider="pacemaker" type="Dummy"/>
    <primitive class="ocf" id="inactive-dummy-2" provider="pacemaker" type="Dummy"/>
  </group>
  <clone id="inactive-clone">
    <primitive id="inactive-dhcpd" class="lsb" type="dhcpd"/>
  </clone>
</resources>
<tags>
  <tag id="inactive-rscs">
    <obj_ref id="inactive-group"/>
    <obj_ref id="inactive-clone"/>
  </tag>
</tags>

The following would be output for crm_mon --resource=inactive-rscs -r:

Cluster Summary:
  * Stack: corosync
  * Current DC: cluster02 (version 2.0.4-1.e97f9675f.git.el7-e97f9675f) - partition with quorum
  * Last updated: Tue Oct 20 16:09:01 2020
  * Last change:  Tue May  5 12:04:36 2020 by hacluster via crmd on cluster01
  * 5 nodes configured
  * 27 resource instances configured (4 DISABLED)

Node List:
  * Online: [ cluster01 cluster02 ]

Full List of Resources:
  * Clone Set: inactive-clone [inactive-dhcpd] (disabled):
    * Stopped (disabled): [ cluster01 cluster02 ]
  * Resource Group: inactive-group (disabled):
    * inactive-dummy-1  (ocf::pacemaker:Dummy):  Stopped (disabled)
    * inactive-dummy-2  (ocf::pacemaker:Dummy):  Stopped (disabled)

12. Utilization and Placement Strategy

Pacemaker decides where to place a resource according to the resource allocation scores on every node. The resource will be allocated to the node where the resource has the highest score.

If the resource allocation scores on all the nodes are equal, by the default placement strategy, Pacemaker will choose a node with the least number of allocated resources for balancing the load. If the number of resources on each node is equal, the first eligible node listed in the CIB will be chosen to run the resource.

Often, in real-world situations, different resources use significantly different proportions of a node’s capacities (memory, I/O, etc.). We cannot balance the load ideally just according to the number of resources allocated to a node. Besides, if resources are placed such that their combined requirements exceed the provided capacity, they may fail to start completely or run with degraded performance.

To take these factors into account, Pacemaker allows you to configure:

  1. The capacity a certain node provides.
  2. The capacity a certain resource requires.
  3. An overall strategy for placement of resources.

12.1. Utilization attributes

To configure the capacity that a node provides or a resource requires, you can use utilization attributes in node and resource objects. You can name utilization attributes according to your preferences and define as many name/value pairs as your configuration needs. However, the attributes’ values must be integers.

Specifying CPU and RAM consumed by several resources

<primitive id="rsc-small" class="ocf" provider="pacemaker" type="Dummy">
  <utilization id="rsc-small-utilization">
    <nvpair id="rsc-small-utilization-cpu" name="cpu" value="1"/>
    <nvpair id="rsc-small-utilization-memory" name="memory" value="1024"/>
  </utilization>
</primitive>
<primitive id="rsc-medium" class="ocf" provider="pacemaker" type="Dummy">
  <utilization id="rsc-medium-utilization">
    <nvpair id="rsc-medium-utilization-cpu" name="cpu" value="2"/>
    <nvpair id="rsc-medium-utilization-memory" name="memory" value="2048"/>
  </utilization>
</primitive>
<primitive id="rsc-large" class="ocf" provider="pacemaker" type="Dummy">
  <utilization id="rsc-large-utilization">
    <nvpair id="rsc-large-utilization-cpu" name="cpu" value="3"/>
    <nvpair id="rsc-large-utilization-memory" name="memory" value="3072"/>
  </utilization>
</primitive>

A node is considered eligible for a resource if it has sufficient free capacity to satisfy the resource’s requirements. The nature of the required or provided capacities is completely irrelevant to Pacemaker – it just makes sure that all capacity requirements of a resource are satisfied before placing a resource to a node.

12.2. Placement Strategy

After you have configured the capacities your nodes provide and the capacities your resources require, you need to set the placement-strategy in the global cluster options, otherwise the capacity configurations have no effect.

Four values are available for the placement-strategy:

  • default

    Utilization values are not taken into account at all. Resources are allocated according to allocation scores. If scores are equal, resources are evenly distributed across nodes.

  • utilization

    Utilization values are taken into account only when deciding whether a node is considered eligible (i.e. whether it has sufficient free capacity to satisfy the resource’s requirements). Load-balancing is still done based on the number of resources allocated to a node.

  • balanced

    Utilization values are taken into account when deciding whether a node is eligible to serve a resource and when load-balancing, so an attempt is made to spread the resources in a way that optimizes resource performance.

  • minimal

    Utilization values are taken into account only when deciding whether a node is eligible to serve a resource. For load-balancing, an attempt is made to concentrate the resources on as few nodes as possible, thereby enabling possible power savings on the remaining nodes.

Set placement-strategy with crm_attribute:

# crm_attribute --name placement-strategy --update balanced

Now Pacemaker will ensure the load from your resources will be distributed evenly throughout the cluster, without the need for convoluted sets of colocation constraints.

12.3. Allocation Details

12.3.1. Which node is preferred to get consumed first when allocating resources?
  • The node with the highest node weight gets consumed first. Node weight is a score maintained by the cluster to represent node health.
  • If multiple nodes have the same node weight:
  • If placement-strategy is default or utilization, the node that has the least number of allocated resources gets consumed first.
    • If their numbers of allocated resources are equal, the first eligible node listed in the CIB gets consumed first.
  • If placement-strategy is balanced, the node that has the most free capacity gets consumed first.
    • If the free capacities of the nodes are equal, the node that has the least number of allocated resources gets consumed first.
      • If their numbers of allocated resources are equal, the first eligible node listed in the CIB gets consumed first.
  • If placement-strategy is minimal, the first eligible node listed in the CIB gets consumed first.
12.3.2. Which node has more free capacity?

If only one type of utilization attribute has been defined, free capacity is a simple numeric comparison.

If multiple types of utilization attributes have been defined, then the node that is numerically highest in the the most attribute types has the most free capacity. For example:

  • If nodeA has more free cpus, and nodeB has more free memory, then their free capacities are equal.
  • If nodeA has more free cpus, while nodeB has more free memory and storage, then nodeB has more free capacity.
12.3.3. Which resource is preferred to be assigned first?
  • The resource that has the highest priority (see Resource Options) gets allocated first.
  • If their priorities are equal, check whether they are already running. The resource that has the highest score on the node where it’s running gets allocated first, to prevent resource shuffling.
  • If the scores above are equal or the resources are not running, the resource has the highest score on the preferred node gets allocated first.
  • If the scores above are equal, the first runnable resource listed in the CIB gets allocated first.

12.4. Limitations and Workarounds

The type of problem Pacemaker is dealing with here is known as the knapsack problem and falls into the NP-complete category of computer science problems – a fancy way of saying “it takes a really long time to solve”.

Clearly in a HA cluster, it’s not acceptable to spend minutes, let alone hours or days, finding an optimal solution while services remain unavailable.

So instead of trying to solve the problem completely, Pacemaker uses a best effort algorithm for determining which node should host a particular service. This means it arrives at a solution much faster than traditional linear programming algorithms, but by doing so at the price of leaving some services stopped.

In the contrived example at the start of this chapter:

  • rsc-small would be allocated to node1
  • rsc-medium would be allocated to node2
  • rsc-large would remain inactive

Which is not ideal.

There are various approaches to dealing with the limitations of pacemaker’s placement strategy:

  • Ensure you have sufficient physical capacity.

    It might sound obvious, but if the physical capacity of your nodes is (close to) maxed out by the cluster under normal conditions, then failover isn’t going to go well. Even without the utilization feature, you’ll start hitting timeouts and getting secondary failures.

  • Build some buffer into the capabilities advertised by the nodes.

    Advertise slightly more resources than we physically have, on the (usually valid) assumption that a resource will not use 100% of the configured amount of CPU, memory and so forth all the time. This practice is sometimes called overcommit.

  • Specify resource priorities.

    If the cluster is going to sacrifice services, it should be the ones you care about (comparatively) the least. Ensure that resource priorities are properly set so that your most important resources are scheduled first.

13. Access Control Lists (ACLs)

By default, the root user or any user in the haclient group can modify Pacemaker’s CIB without restriction. Pacemaker offers access control lists (ACLs) to provide more fine-grained authorization.

Important

Being able to modify the CIB’s resource section allows a user to run any executable file as root, by configuring it as an LSB resource with a full path.

13.1. ACL Prerequisites

In order to use ACLs:

  • The Pacemaker software must have been built with ACL support. If the output of the command pacemakerd --features contains acls, your installation supports ACLs.
  • Desired users must have user accounts in the haclient group on all cluster nodes in the cluster.
  • If your CIB was created before Pacemaker 1.1.12, it might need to be updated to the current schema (using cibadmin --upgrade or a higher-level tool equivalent) in order to use the syntax documented here.
  • The enable-acl cluster option must be set to true.

13.2. ACL Configuration

ACLs are specified within an acls element of the CIB. The acls element may contain any number of acl_role, acl_target, and acl_group elements.

13.3. ACL Roles

An ACL role is a collection of permissions allowing or denying access to particular portions of the CIB. A role is configured with an acl_role element in the CIB acls section.

Properties of an acl_role element
Attribute Description
id

A unique name for the role (required)

description

Arbitrary text (not used by Pacemaker)

An acl_role element may contain any number of acl_permission elements.

Properties of an acl_permission element
Attribute Description
id

A unique name for the permission (required)

description

Arbitrary text (not used by Pacemaker)

kind

The access being granted. Allowed values are read, write, and deny. A value of write grants both read and write access.

object-type

The name of an XML element in the CIB to which the permission applies. (Exactly one of object-type, xpath, and reference must be specified for a permission.)

attribute

If specified, the permission applies only to object-type elements that have this attribute set (to any value). If not specified, the permission applies to all object-type elements. May only be used with object-type.

reference

The ID of an XML element in the CIB to which the permission applies. (Exactly one of object-type, xpath, and reference must be specified for a permission.)

xpath

An XPath specification selecting an XML element in the CIB to which the permission applies. Attributes may be specified in the XPath to select particular elements, but the permissions apply to the entire element. (Exactly one of object-type, xpath, and reference must be specified for a permission.)

Important

  • Permissions are applied to the selected XML element’s entire XML subtree (all elements enclosed within it).
  • Write permission grants the ability to create, modify, or remove the element and its subtree, and also the ability to create any “scaffolding” elements (enclosing elements that do not have attributes other than an ID).
  • Permissions for more specific matches (more deeply nested elements) take precedence over more general ones.
  • If multiple permissions are configured for the same match (for example, in different roles applied to the same user), any deny permission takes precedence, then write, then lastly read.

13.4. ACL Targets and Groups

ACL targets correspond to user accounts on the system.

Properties of an acl_target element
Attribute Description
id

The name of a user on the system (required)

ACL groups may be specified, but are not currently used by Pacemaker. This is expected to change in a future version.

Properties of an acl_group element
Attribute Description
id

The name of a group on the system (required)

Each acl_target and acl_group element may contain any number of role elements.

Properties of a role element
Attribute Description
id

The id of an acl_role element that specifies permissions granted to the enclosing target or group.

Important

The root and hacluster user accounts always have full access to the CIB, regardless of ACLs. For all other user accounts, when enable-acl is true, permission to all parts of the CIB is denied by default (permissions must be explicitly granted).

13.5. ACL Examples

<acls>

   <acl_role id="read_all">
       <acl_permission id="read_all-cib" kind="read" xpath="/cib" />
   </acl_role>

   <acl_role id="operator">

       <acl_permission id="operator-maintenance-mode" kind="write"
           xpath="//crm_config//nvpair[@name='maintenance-mode']" />

       <acl_permission id="operator-maintenance-attr" kind="write"
           xpath="//nvpair[@name='maintenance']" />

       <acl_permission id="operator-target-role" kind="write"
           xpath="//resources//meta_attributes/nvpair[@name='target-role']" />

       <acl_permission id="operator-is-managed" kind="write"
           xpath="//resources//nvpair[@name='is-managed']" />

       <acl_permission id="operator-rsc_location" kind="write"
           object-type="rsc_location" />

   </acl_role>

   <acl_role id="administrator">
       <acl_permission id="administrator-cib" kind="write" xpath="/cib" />
   </acl_role>

   <acl_role id="minimal">

       <acl_permission id="minimal-standby" kind="read"
           description="allow reading standby node attribute (permanent or transient)"
           xpath="//instance_attributes/nvpair[@name='standby']"/>

       <acl_permission id="minimal-maintenance" kind="read"
           description="allow reading maintenance node attribute (permanent or transient)"
           xpath="//nvpair[@name='maintenance']"/>

       <acl_permission id="minimal-target-role" kind="read"
           description="allow reading resource target roles"
           xpath="//resources//meta_attributes/nvpair[@name='target-role']"/>

       <acl_permission id="minimal-is-managed" kind="read"
           description="allow reading resource managed status"
           xpath="//resources//meta_attributes/nvpair[@name='is-managed']"/>

       <acl_permission id="minimal-deny-instance-attributes" kind="deny"
           xpath="//instance_attributes"/>

       <acl_permission id="minimal-deny-meta-attributes" kind="deny"
           xpath="//meta_attributes"/>

       <acl_permission id="minimal-deny-operations" kind="deny"
           xpath="//operations"/>

       <acl_permission id="minimal-deny-utilization" kind="deny"
           xpath="//utilization"/>

       <acl_permission id="minimal-nodes" kind="read"
           description="allow reading node names/IDs (attributes are denied separately)"
           xpath="/cib/configuration/nodes"/>

       <acl_permission id="minimal-resources" kind="read"
           description="allow reading resource names/agents (parameters are denied separately)"
           xpath="/cib/configuration/resources"/>

       <acl_permission id="minimal-deny-constraints" kind="deny"
           xpath="/cib/configuration/constraints"/>

       <acl_permission id="minimal-deny-topology" kind="deny"
           xpath="/cib/configuration/fencing-topology"/>

       <acl_permission id="minimal-deny-op_defaults" kind="deny"
           xpath="/cib/configuration/op_defaults"/>

       <acl_permission id="minimal-deny-rsc_defaults" kind="deny"
           xpath="/cib/configuration/rsc_defaults"/>

       <acl_permission id="minimal-deny-alerts" kind="deny"
           xpath="/cib/configuration/alerts"/>

       <acl_permission id="minimal-deny-acls" kind="deny"
           xpath="/cib/configuration/acls"/>

       <acl_permission id="minimal-cib" kind="read"
           description="allow reading cib element and crm_config/status sections"
           xpath="/cib"/>

   </acl_role>

   <acl_target id="alice">
      <role id="minimal"/>
   </acl_target>

   <acl_target id="bob">
      <role id="read_all"/>
   </acl_target>

   <acl_target id="carol">
      <role id="read_all"/>
      <role id="operator"/>
   </acl_target>

   <acl_target id="dave">
      <role id="administrator"/>
   </acl_target>

</acls>

In the above example, the user alice has the minimal permissions necessary to run basic Pacemaker CLI tools, including using crm_mon to view the cluster status, without being able to modify anything. The user bob can view the entire configuration and status of the cluster, but not make any changes. The user carol can read everything, and change selected cluster properties as well as resource roles and location constraints. Finally, dave has full read and write access to the entire CIB.

Looking at the minimal role in more depth, it is designed to allow read access to the cib tag itself, while denying access to particular portions of its subtree (which is the entire CIB).

This is because the DC node is indicated in the cib tag, so crm_mon will not be able to report the DC otherwise. However, this does change the security model to allow by default, since any portions of the CIB not explicitly denied will be readable. The cib read access could be removed and replaced with read access to just the crm_config and status sections, for a safer approach at the cost of not seeing the DC in status output.

For a simpler configuration, the minimal role allows read access to the entire crm_config section, which contains cluster properties. It would be possible to allow read access to specific properties instead (such as stonith-enabled, dc-uuid, have-quorum, and cluster-name) to restrict access further while still allowing status output, but cluster properties are unlikely to be considered sensitive.

13.6. ACL Limitations

13.6.1. Actions performed via IPC rather than the CIB

ACLs apply only to the CIB.

That means ACLs apply to command-line tools that operate by reading or writing the CIB, such as crm_attribute when managing permanent node attributes, crm_mon, and cibadmin.

However, command-line tools that communicate directly with Pacemaker daemons via IPC are not affected by ACLs. For example, users in the haclient group may still do the following, regardless of ACLs:

  • Query transient node attribute values using crm_attribute and attrd_updater.
  • Query basic node information using crm_node.
  • Erase resource operation history using crm_resource.
  • Query fencing configuration information, and execute fencing against nodes, using stonith_admin.
13.6.2. ACLs and Pacemaker Remote

ACLs apply to commands run on Pacemaker Remote nodes using the Pacemaker Remote node’s name as the ACL user name.

The idea is that Pacemaker Remote nodes (especially virtual machines and containers) are likely to be purpose-built and have different user accounts from full cluster nodes.

14. Status – Here be dragons

Most users never need to understand the contents of the status section and can be happy with the output from crm_mon.

However for those with a curious inclination, this section attempts to provide an overview of its contents.

14.1. Node Status

In addition to the cluster’s configuration, the CIB holds an up-to-date representation of each cluster node in the status section.

A bare-bones status entry for a healthy node cl-virt-1

<node_state id="1" uname="cl-virt-1" in_ccm="true" crmd="online" crm-debug-origin="do_update_resource" join="member" expected="member">
 <transient_attributes id="1"/>
 <lrm id="1"/>
</node_state>

Users are highly recommended not to modify any part of a node’s state directly. The cluster will periodically regenerate the entire section from authoritative sources, so any changes should be done with the tools appropriate to those sources.

Authoritative Sources for State Information
CIB Object Authoritative Source
node_state pacemaker-controld
transient_attributes pacemaker-attrd
lrm pacemaker-execd

The fields used in the node_state objects are named as they are largely for historical reasons and are rooted in Pacemaker’s origins as the resource manager for the older Heartbeat project. They have remained unchanged to preserve compatibility with older versions.

Node Status Fields
Field Description
id Unique identifier for the node. Corosync-based clusters use a numeric counter.
uname

The node’s name as known by the cluster

in_ccm

Is the node a member at the cluster communication later? Allowed values: true, false.

crmd

Is the node a member at the pacemaker layer? Allowed values: online, offline.

crm-debug-origin

The name of the source function that made the most recent change (for debugging purposes).

join

Does the node participate in hosting resources? Allowed values: down, pending, member. banned.

expected

Expected value for join.

The cluster uses these fields to determine whether, at the node level, the node is healthy or is in a failed state and needs to be fenced.

14.2. Transient Node Attributes

Like regular Node Attributes, the name/value pairs listed in the transient_attributes section help to describe the node. However they are forgotten by the cluster when the node goes offline. This can be useful, for instance, when you want a node to be in standby mode (not able to run resources) just until the next reboot.

In addition to any values the administrator sets, the cluster will also store information about failed resources here.

A set of transient node attributes for node cl-virt-1

<transient_attributes id="cl-virt-1">
  <instance_attributes id="status-cl-virt-1">
     <nvpair id="status-cl-virt-1-pingd" name="pingd" value="3"/>
     <nvpair id="status-cl-virt-1-probe_complete" name="probe_complete" value="true"/>
     <nvpair id="status-cl-virt-1-fail-count-pingd:0.monitor_30000" name="fail-count-pingd:0#monitor_30000" value="1"/>
     <nvpair id="status-cl-virt-1-last-failure-pingd:0" name="last-failure-pingd:0" value="1239009742"/>
  </instance_attributes>
</transient_attributes>

In the above example, we can see that a monitor on the pingd:0 resource has failed once, at 09:22:22 UTC 6 April 2009. [1].

We also see that the node is connected to three pingd peers and that all known resources have been checked for on this machine (probe_complete).

14.3. Operation History

A node’s resource history is held in the lrm_resources tag (a child of the lrm tag). The information stored here includes enough information for the cluster to stop the resource safely if it is removed from the configuration section. Specifically, the resource’s id, class, type and provider are stored.

A record of the apcstonith resource

<lrm_resource id="apcstonith" type="fence_apc_snmp" class="stonith"/>

Additionally, we store the last job for every combination of resource, action and interval. The concatenation of the values in this tuple are used to create the id of the lrm_rsc_op object.

Contents of an lrm_rsc_op job
Field Description
id

Identifier for the job constructed from the resource’s operation and interval.

call-id

The job’s ticket number. Used as a sort key to determine the order in which the jobs were executed.

operation

The action the resource agent was invoked with.

interval

The frequency, in milliseconds, at which the operation will be repeated. A one-off job is indicated by 0.

op-status

The job’s status. Generally this will be either 0 (done) or -1 (pending). Rarely used in favor of rc-code.

rc-code

The job’s result. Refer to the Resource Agents chapter of Pacemaker Administration for details on what the values here mean and how they are interpreted.

last-rc-change

Machine-local date/time, in seconds since epoch, at which the job first returned the current value of rc-code. For diagnostic purposes.

exec-time

Time, in milliseconds, that the job was running for. For diagnostic purposes.

queue-time

Time, in seconds, that the job was queued for in the local executor. For diagnostic purposes.

crm_feature_set

The version which this job description conforms to. Used when processing op-digest.

transition-key

A concatenation of the job’s graph action number, the graph number, the expected result and the UUID of the controller instance that scheduled it. This is used to construct transition-magic (below).

transition-magic

A concatenation of the job’s op-status, rc-code and transition-key. Guaranteed to be unique for the life of the cluster (which ensures it is part of CIB update notifications) and contains all the information needed for the controller to correctly analyze and process the completed job. Most importantly, the decomposed elements tell the controller if the job entry was expected and whether it failed.

op-digest

An MD5 sum representing the parameters passed to the job. Used to detect changes to the configuration, to restart resources if necessary.

crm-debug-origin

The origin of the current values. For diagnostic purposes.

14.3.1. Simple Operation History Example

A monitor operation (determines current state of the apcstonith resource)

<lrm_resource id="apcstonith" type="fence_apc_snmp" class="stonith">
  <lrm_rsc_op id="apcstonith_monitor_0" operation="monitor" call-id="2"
    rc-code="7" op-status="0" interval="0"
    crm-debug-origin="do_update_resource" crm_feature_set="3.0.1"
    op-digest="2e3da9274d3550dc6526fb24bfcbcba0"
    transition-key="22:2:7:2668bbeb-06d5-40f9-936d-24cb7f87006a"
    transition-magic="0:7;22:2:7:2668bbeb-06d5-40f9-936d-24cb7f87006a"
    last-rc-change="1239008085" exec-time="10" queue-time="0"/>
</lrm_resource>

In the above example, the job is a non-recurring monitor operation often referred to as a “probe” for the apcstonith resource.

The cluster schedules probes for every configured resource on a node when the node first starts, in order to determine the resource’s current state before it takes any further action.

From the transition-key, we can see that this was the 22nd action of the 2nd graph produced by this instance of the controller (2668bbeb-06d5-40f9-936d-24cb7f87006a).

The third field of the transition-key contains a 7, which indicates that the job expects to find the resource inactive. By looking at the rc-code property, we see that this was the case.

As that is the only job recorded for this node, we can conclude that the cluster started the resource elsewhere.

14.3.2. Complex Operation History Example

Resource history of a pingd clone with multiple jobs

<lrm_resource id="pingd:0" type="pingd" class="ocf" provider="pacemaker">
  <lrm_rsc_op id="pingd:0_monitor_30000" operation="monitor" call-id="34"
    rc-code="0" op-status="0" interval="30000"
    crm-debug-origin="do_update_resource" crm_feature_set="3.0.1"
    transition-key="10:11:0:2668bbeb-06d5-40f9-936d-24cb7f87006a"
    last-rc-change="1239009741" exec-time="10" queue-time="0"/>
  <lrm_rsc_op id="pingd:0_stop_0" operation="stop"
    crm-debug-origin="do_update_resource" crm_feature_set="3.0.1" call-id="32"
    rc-code="0" op-status="0" interval="0"
    transition-key="11:11:0:2668bbeb-06d5-40f9-936d-24cb7f87006a"
    last-rc-change="1239009741" exec-time="10" queue-time="0"/>
  <lrm_rsc_op id="pingd:0_start_0" operation="start" call-id="33"
    rc-code="0" op-status="0" interval="0"
    crm-debug-origin="do_update_resource" crm_feature_set="3.0.1"
    transition-key="31:11:0:2668bbeb-06d5-40f9-936d-24cb7f87006a"
    last-rc-change="1239009741" exec-time="10" queue-time="0" />
  <lrm_rsc_op id="pingd:0_monitor_0" operation="monitor" call-id="3"
    rc-code="0" op-status="0" interval="0"
    crm-debug-origin="do_update_resource" crm_feature_set="3.0.1"
    transition-key="23:2:7:2668bbeb-06d5-40f9-936d-24cb7f87006a"
    last-rc-change="1239008085" exec-time="20" queue-time="0"/>
  </lrm_resource>

When more than one job record exists, it is important to first sort them by call-id before interpreting them.

Once sorted, the above example can be summarized as:

  1. A non-recurring monitor operation returning 7 (not running), with a call-id of 3
  2. A stop operation returning 0 (success), with a call-id of 32
  3. A start operation returning 0 (success), with a call-id of 33
  4. A recurring monitor returning 0 (success), with a call-id of 34

The cluster processes each job record to build up a picture of the resource’s state. After the first and second entries, it is considered stopped, and after the third it considered active.

Based on the last operation, we can tell that the resource is currently active.

Additionally, from the presence of a stop operation with a lower call-id than that of the start operation, we can conclude that the resource has been restarted. Specifically this occurred as part of actions 11 and 31 of transition 11 from the controller instance with the key 2668bbeb.... This information can be helpful for locating the relevant section of the logs when looking for the source of a failure.

[1]You can use the standard date command to print a human-readable version of any seconds-since-epoch value, for example date -d @1239009742.

15. Multi-Site Clusters and Tickets

Apart from local clusters, Pacemaker also supports multi-site clusters. That means you can have multiple, geographically dispersed sites, each with a local cluster. Failover between these clusters can be coordinated manually by the administrator, or automatically by a higher-level entity called a Cluster Ticket Registry (CTR).

15.1. Challenges for Multi-Site Clusters

Typically, multi-site environments are too far apart to support synchronous communication and data replication between the sites. That leads to significant challenges:

  • How do we make sure that a cluster site is up and running?
  • How do we make sure that resources are only started once?
  • How do we make sure that quorum can be reached between the different sites and a split-brain scenario avoided?
  • How do we manage failover between sites?
  • How do we deal with high latency in case of resources that need to be stopped?

In the following sections, learn how to meet these challenges.

15.2. Conceptual Overview

Multi-site clusters can be considered as “overlay” clusters where each cluster site corresponds to a cluster node in a traditional cluster. The overlay cluster can be managed by a CTR in order to guarantee that any cluster resource will be active on no more than one cluster site. This is achieved by using tickets that are treated as failover domain between cluster sites, in case a site should be down.

The following sections explain the individual components and mechanisms that were introduced for multi-site clusters in more detail.

15.2.1. Ticket

Tickets are, essentially, cluster-wide attributes. A ticket grants the right to run certain resources on a specific cluster site. Resources can be bound to a certain ticket by rsc_ticket constraints. Only if the ticket is available at a site can the respective resources be started there. Vice versa, if the ticket is revoked, the resources depending on that ticket must be stopped.

The ticket thus is similar to a site quorum, i.e. the permission to manage/own resources associated with that site. (One can also think of the current have-quorum flag as a special, cluster-wide ticket that is granted in case of node majority.)

Tickets can be granted and revoked either manually by administrators (which could be the default for classic enterprise clusters), or via the automated CTR mechanism described below.

A ticket can only be owned by one site at a time. Initially, none of the sites has a ticket. Each ticket must be granted once by the cluster administrator.

The presence or absence of tickets for a site is stored in the CIB as a cluster status. With regards to a certain ticket, there are only two states for a site: true (the site has the ticket) or false (the site does not have the ticket). The absence of a certain ticket (during the initial state of the multi-site cluster) is the same as the value false.

15.2.2. Dead Man Dependency

A site can only activate resources safely if it can be sure that the other site has deactivated them. However after a ticket is revoked, it can take a long time until all resources depending on that ticket are stopped “cleanly”, especially in case of cascaded resources. To cut that process short, the concept of a Dead Man Dependency was introduced.

If a dead man dependency is in force, if a ticket is revoked from a site, the nodes that are hosting dependent resources are fenced. This considerably speeds up the recovery process of the cluster and makes sure that resources can be migrated more quickly.

This can be configured by specifying a loss-policy="fence" in rsc_ticket constraints.

15.2.3. Cluster Ticket Registry

A CTR is a coordinated group of network daemons that automatically handles granting, revoking, and timing out tickets (instead of the administrator revoking the ticket somewhere, waiting for everything to stop, and then granting it on the desired site).

Pacemaker does not implement its own CTR, but interoperates with external software designed for that purpose (similar to how resource and fencing agents are not directly part of pacemaker).

Participating clusters run the CTR daemons, which connect to each other, exchange information about their connectivity, and vote on which sites gets which tickets.

A ticket is granted to a site only once the CTR is sure that the ticket has been relinquished by the previous owner, implemented via a timer in most scenarios. If a site loses connection to its peers, its tickets time out and recovery occurs. After the connection timeout plus the recovery timeout has passed, the other sites are allowed to re-acquire the ticket and start the resources again.

This can also be thought of as a “quorum server”, except that it is not a single quorum ticket, but several.

15.2.4. Configuration Replication

As usual, the CIB is synchronized within each cluster, but it is not synchronized across cluster sites of a multi-site cluster. You have to configure the resources that will be highly available across the multi-site cluster for every site accordingly.

15.3. Configuring Ticket Dependencies

The rsc_ticket constraint lets you specify the resources depending on a certain ticket. Together with the constraint, you can set a loss-policy that defines what should happen to the respective resources if the ticket is revoked.

The attribute loss-policy can have the following values:

  • fence: Fence the nodes that are running the relevant resources.
  • stop: Stop the relevant resources.
  • freeze: Do nothing to the relevant resources.
  • demote: Demote relevant resources that are running in the promoted role.

Constraint that fences node if ticketA is revoked

<rsc_ticket id="rsc1-req-ticketA" rsc="rsc1" ticket="ticketA" loss-policy="fence"/>

The example above creates a constraint with the ID rsc1-req-ticketA. It defines that the resource rsc1 depends on ticketA and that the node running the resource should be fenced if ticketA is revoked.

If resource rsc1 were a promotable resource, you might want to configure that only being in the promoted role depends on ticketA. With the following configuration, rsc1 will be demoted if ticketA is revoked:

Constraint that demotes rsc1 if ticketA is revoked

<rsc_ticket id="rsc1-req-ticketA" rsc="rsc1" rsc-role="Promoted" ticket="ticketA" loss-policy="demote"/>

You can create multiple rsc_ticket constraints to let multiple resources depend on the same ticket. However, rsc_ticket also supports resource sets (see Resource Sets), so one can easily list all the resources in one rsc_ticket constraint instead.

Ticket constraint for multiple resources

<rsc_ticket id="resources-dep-ticketA" ticket="ticketA" loss-policy="fence">
  <resource_set id="resources-dep-ticketA-0" role="Started">
    <resource_ref id="rsc1"/>
    <resource_ref id="group1"/>
    <resource_ref id="clone1"/>
  </resource_set>
  <resource_set id="resources-dep-ticketA-1" role="Promoted">
    <resource_ref id="ms1"/>
  </resource_set>
</rsc_ticket>

In the example above, there are two resource sets, so we can list resources with different roles in a single rsc_ticket constraint. There’s no dependency between the two resource sets, and there’s no dependency among the resources within a resource set. Each of the resources just depends on ticketA.

Referencing resource templates in rsc_ticket constraints, and even referencing them within resource sets, is also supported.

If you want other resources to depend on further tickets, create as many constraints as necessary with rsc_ticket.

15.4. Managing Multi-Site Clusters

15.4.1. Granting and Revoking Tickets Manually

You can grant tickets to sites or revoke them from sites manually. If you want to re-distribute a ticket, you should wait for the dependent resources to stop cleanly at the previous site before you grant the ticket to the new site.

Use the crm_ticket command line tool to grant and revoke tickets.

To grant a ticket to this site:

# crm_ticket --ticket ticketA --grant

To revoke a ticket from this site:

# crm_ticket --ticket ticketA --revoke

Important

If you are managing tickets manually, use the crm_ticket command with great care, because it cannot check whether the same ticket is already granted elsewhere.

15.4.2. Granting and Revoking Tickets via a Cluster Ticket Registry

We will use Booth here as an example of software that can be used with pacemaker as a Cluster Ticket Registry. Booth implements the Raft algorithm to guarantee the distributed consensus among different cluster sites, and manages the ticket distribution (and thus the failover process between sites).

Each of the participating clusters and arbitrators runs the Booth daemon boothd.

An arbitrator is the multi-site equivalent of a quorum-only node in a local cluster. If you have a setup with an even number of sites, you need an additional instance to reach consensus about decisions such as failover of resources across sites. In this case, add one or more arbitrators running at additional sites. Arbitrators are single machines that run a booth instance in a special mode. An arbitrator is especially important for a two-site scenario, otherwise there is no way for one site to distinguish between a network failure between it and the other site, and a failure of the other site.

The most common multi-site scenario is probably a multi-site cluster with two sites and a single arbitrator on a third site. However, technically, there are no limitations with regards to the number of sites and the number of arbitrators involved.

Boothd at each site connects to its peers running at the other sites and exchanges connectivity details. Once a ticket is granted to a site, the booth mechanism will manage the ticket automatically: If the site which holds the ticket is out of service, the booth daemons will vote which of the other sites will get the ticket. To protect against brief connection failures, sites that lose the vote (either explicitly or implicitly by being disconnected from the voting body) need to relinquish the ticket after a time-out. Thus, it is made sure that a ticket will only be re-distributed after it has been relinquished by the previous site. The resources that depend on that ticket will fail over to the new site holding the ticket. The nodes that have run the resources before will be treated according to the loss-policy you set within the rsc_ticket constraint.

Before the booth can manage a certain ticket within the multi-site cluster, you initially need to grant it to a site manually via the booth command-line tool. After you have initially granted a ticket to a site, boothd will take over and manage the ticket automatically.

Important

The booth command-line tool can be used to grant, list, or revoke tickets and can be run on any machine where boothd is running. If you are managing tickets via Booth, use only booth for manual intervention, not crm_ticket. That ensures the same ticket will only be owned by one cluster site at a time.

15.4.2.1. Booth Requirements
  • All clusters that will be part of the multi-site cluster must be based on Pacemaker.
  • Booth must be installed on all cluster nodes and on all arbitrators that will be part of the multi-site cluster.
  • Nodes belonging to the same cluster site should be synchronized via NTP. However, time synchronization is not required between the individual cluster sites.
15.4.3. General Management of Tickets

Display the information of tickets:

# crm_ticket --info

Or you can monitor them with:

# crm_mon --tickets

Display the rsc_ticket constraints that apply to a ticket:

# crm_ticket --ticket ticketA --constraints

When you want to do maintenance or manual switch-over of a ticket, revoking the ticket would trigger the loss policies. If loss-policy="fence", the dependent resources could not be gracefully stopped/demoted, and other unrelated resources could even be affected.

The proper way is making the ticket standby first with:

# crm_ticket --ticket ticketA --standby

Then the dependent resources will be stopped or demoted gracefully without triggering the loss policies.

If you have finished the maintenance and want to activate the ticket again, you can run:

# crm_ticket --ticket ticketA --activate

15.5. For more information

16. Sample Configurations

16.1. Empty

An Empty Configuration

<cib crm_feature_set="3.0.7" validate-with="pacemaker-1.2" admin_epoch="1" epoch="0" num_updates="0">
  <configuration>
    <crm_config/>
    <nodes/>
    <resources/>
    <constraints/>
  </configuration>
  <status/>
</cib>

16.2. Simple

A simple configuration with two nodes, some cluster options and a resource

<cib crm_feature_set="3.0.7" validate-with="pacemaker-1.2" admin_epoch="1" epoch="0" num_updates="0">
  <configuration>
    <crm_config>
      <cluster_property_set id="cib-bootstrap-options">
        <nvpair id="option-1" name="symmetric-cluster" value="true"/>
        <nvpair id="option-2" name="no-quorum-policy" value="stop"/>
        <nvpair id="option-3" name="stonith-enabled" value="0"/>
      </cluster_property_set>
    </crm_config>
    <nodes>
      <node id="xxx" uname="c001n01" type="normal"/>
      <node id="yyy" uname="c001n02" type="normal"/>
    </nodes>
    <resources>
      <primitive id="myAddr" class="ocf" provider="heartbeat" type="IPaddr">
        <operations>
          <op id="myAddr-monitor" name="monitor" interval="300s"/>
        </operations>
        <instance_attributes id="myAddr-params">
          <nvpair id="myAddr-ip" name="ip" value="192.0.2.10"/>
        </instance_attributes>
      </primitive>
    </resources>
    <constraints>
      <rsc_location id="myAddr-prefer" rsc="myAddr" node="c001n01" score="INFINITY"/>
    </constraints>
    <rsc_defaults>
      <meta_attributes id="rsc_defaults-options">
        <nvpair id="rsc-default-1" name="resource-stickiness" value="100"/>
        <nvpair id="rsc-default-2" name="migration-threshold" value="10"/>
      </meta_attributes>
    </rsc_defaults>
    <op_defaults>
      <meta_attributes id="op_defaults-options">
        <nvpair id="op-default-1" name="timeout" value="30s"/>
      </meta_attributes>
    </op_defaults>
  </configuration>
  <status/>
</cib>

In the above example, we have one resource (an IP address) that we check every five minutes and will run on host c001n01 until either the resource fails 10 times or the host shuts down.

16.3. Advanced Configuration

An advanced configuration with groups, clones and STONITH

<cib crm_feature_set="3.0.7" validate-with="pacemaker-1.2" admin_epoch="1" epoch="0" num_updates="0">
  <configuration>
    <crm_config>
      <cluster_property_set id="cib-bootstrap-options">
        <nvpair id="option-1" name="symmetric-cluster" value="true"/>
        <nvpair id="option-2" name="no-quorum-policy" value="stop"/>
        <nvpair id="option-3" name="stonith-enabled" value="true"/>
      </cluster_property_set>
    </crm_config>
    <nodes>
      <node id="xxx" uname="c001n01" type="normal"/>
      <node id="yyy" uname="c001n02" type="normal"/>
      <node id="zzz" uname="c001n03" type="normal"/>
    </nodes>
    <resources>
      <primitive id="myAddr" class="ocf" provider="heartbeat" type="IPaddr">
        <operations>
          <op id="myAddr-monitor" name="monitor" interval="300s"/>
        </operations>
        <instance_attributes id="myAddr-attrs">
          <nvpair id="myAddr-attr-1" name="ip" value="192.0.2.10"/>
        </instance_attributes>
      </primitive>
      <group id="myGroup">
        <primitive id="database" class="lsb" type="oracle">
          <operations>
            <op id="database-monitor" name="monitor" interval="300s"/>
          </operations>
        </primitive>
        <primitive id="webserver" class="lsb" type="apache">
          <operations>
            <op id="webserver-monitor" name="monitor" interval="300s"/>
          </operations>
        </primitive>
      </group>
      <clone id="STONITH">
        <meta_attributes id="stonith-options">
          <nvpair id="stonith-option-1" name="globally-unique" value="false"/>
        </meta_attributes>
        <primitive id="stonithclone" class="stonith" type="external/ssh">
          <operations>
            <op id="stonith-op-mon" name="monitor" interval="5s"/>
          </operations>
          <instance_attributes id="stonith-attrs">
            <nvpair id="stonith-attr-1" name="hostlist" value="c001n01,c001n02"/>
          </instance_attributes>
        </primitive>
      </clone>
    </resources>
    <constraints>
      <rsc_location id="myAddr-prefer" rsc="myAddr" node="c001n01"
        score="INFINITY"/>
      <rsc_colocation id="group-with-ip" rsc="myGroup" with-rsc="myAddr"
        score="INFINITY"/>
    </constraints>
    <op_defaults>
      <meta_attributes id="op_defaults-options">
        <nvpair id="op-default-1" name="timeout" value="30s"/>
      </meta_attributes>
    </op_defaults>
    <rsc_defaults>
      <meta_attributes id="rsc_defaults-options">
        <nvpair id="rsc-default-1" name="resource-stickiness" value="100"/>
        <nvpair id="rsc-default-2" name="migration-threshold" value="10"/>
      </meta_attributes>
    </rsc_defaults>
  </configuration>
  <status/>
</cib>