4. Remote Node Walk-through

What this tutorial is: An in-depth walk-through of how to get Pacemaker to integrate a remote node into the cluster as a node capable of running cluster resources.

What this tutorial is not: A realistic deployment scenario. The steps shown here are meant to get users familiar with the concept of remote nodes as quickly as possible.

4.1. Configure Cluster Nodes

This walk-through assumes you already have a Pacemaker cluster configured. For examples, we will use a cluster with two cluster nodes named pcmk-1 and pcmk-2. You can substitute whatever your node names are, for however many nodes you have. If you are not familiar with setting up basic Pacemaker clusters, follow the walk-through in the Clusters From Scratch document before attempting this one.

You will need to add the remote node’s hostname (we’re using remote1 in this tutorial) to the cluster nodes’ /etc/hosts files if you haven’t already. This is required unless you have DNS set up in a way where remote1’s address can be discovered.

Execute the following on each cluster node, replacing the IP address with the actual IP address of the remote node.

# cat << END >> /etc/hosts
192.168.122.10    remote1
END

4.2. Configure Remote Node

4.2.1. Configure Firewall on Remote Node

Allow cluster-related services through the local firewall:

# firewall-cmd --permanent --add-service=high-availability
success
# firewall-cmd --reload
success

Note

If you are using some other firewall solution besides firewalld, simply open the following ports, which can be used by various clustering components: TCP ports 2224, 3121, and 21064, and UDP port 5405.

If you run into any problems during testing, you might want to disable the firewall and SELinux entirely until you have everything working. This may create significant security issues and should not be performed on machines that will be exposed to the outside world, but may be appropriate during development and testing on a protected host.

To disable security measures:

# setenforce 0
# sed -i.bak "s/SELINUX=enforcing/SELINUX=permissive/g" /etc/selinux/config
# systemctl mask firewalld.service
# systemctl stop firewalld.service

4.2.2. Configure pacemaker_remote on Remote Node

Install the pacemaker_remote daemon on the remote node.

# yum install -y pacemaker-remote resource-agents pcs

4.2.3. Integrate Remote Node into Cluster

Integrating a remote node into the cluster is achieved through the creation of a remote node connection resource. The remote node connection resource both establishes the connection to the remote node and defines that the remote node exists. Note that this resource is actually internal to Pacemaker’s controller. A metadata file for this resource can be found in the /usr/lib/ocf/resource.d/pacemaker/remote file that describes what options are available, but there is no actual ocf:pacemaker:remote resource agent script that performs any work.

Before we integrate the remote node, we’ll need to authorize it.

# pcs host auth remote1

Now, define the remote node connection resource to our remote node, remote1, using the following command on any cluster node. This command creates the ocf:pacemaker:remote resource, creates and copies the key, and enables pacemaker_remote.

# pcs cluster node add-remote remote1

That’s it. After a moment you should see the remote node come online. The final pcs status output should look something like this, and you can see that it created the ocf:pacemaker:remote resource:

# pcs status
Cluster name: mycluster
Cluster Summary:
  * Stack: corosync
  * Current DC: pcmk-1 (version 2.0.5-8.el8-ba59be7122) - partition with quorum
  * Last updated: Wed Mar  3 11:02:03 2021
  * Last change:  Wed Mar  3 11:01:57 2021 by root via cibadmin on pcmk-1
  * 3 nodes configured
  * 1 resource instance configured

Node List:
  * Online: [ pcmk-1 pcmk-2 ]
  * RemoteOnline: [ remote1 ]

Full List of Resources:
  * remote1 (ocf::pacemaker:remote):         Started pcmk-1

4.3. How pcs Configures the Remote

To see that it created the key and copied it to all cluster nodes and the guest, run:

# ls -l /etc/pacemaker

To see that it enables pacemaker_remote, run:

# systemctl status pacemaker_remote
● pacemaker_remote.service - Pacemaker Remote executor daemon
   Loaded: loaded (/usr/lib/systemd/system/pacemaker_remote.service; enabled; vendor preset: disabled)
   Active: active (running) since Tue 2021-03-02 10:42:40 EST; 1min 23s ago
     Docs: man:pacemaker-remoted
           https://clusterlabs.org/pacemaker/doc/
 Main PID: 1139 (pacemaker-remot)
    Tasks: 1
   Memory: 5.4M
   CGroup: /system.slice/pacemaker_remote.service
           └─1139 /usr/sbin/pacemaker-remoted

Mar 02 10:42:40 remote1 systemd[1]: Started Pacemaker Remote executor daemon.
Mar 02 10:42:40 remote1 pacemaker-remoted[1139]:  notice: Additional logging available in /var/log/pacemaker/pacemaker.log
Mar 02 10:42:40 remote1 pacemaker-remoted[1139]:  notice: Starting Pacemaker remote executor
Mar 02 10:42:41 remote1 pacemaker-remoted[1139]:  notice: Pacemaker remote executor successfully started and accepting connections

4.4. Starting Resources on Remote Node

Once the remote node is integrated into the cluster, starting resources on a remote node is the exact same as on cluster nodes. Refer to the Clusters from Scratch document for examples of resource creation.

Warning

Never involve a remote node connection resource in a resource group, colocation constraint, or order constraint.

4.5. Fencing Remote Nodes

Remote nodes are fenced the same way as cluster nodes. No special considerations are required. Configure fencing resources for use with remote nodes the same as you would with cluster nodes.

Note, however, that remote nodes can never ‘initiate’ a fencing action. Only cluster nodes are capable of actually executing a fencing operation against another node.

4.6. Accessing Cluster Tools from a Remote Node

Besides allowing the cluster to manage resources on a remote node, pacemaker_remote has one other trick. The pacemaker_remote daemon allows nearly all the pacemaker tools (crm_resource, crm_mon, crm_attribute, etc.) to work on remote nodes natively.

Try it: Run crm_mon on the remote node after pacemaker has integrated it into the cluster. These tools just work. These means resource agents such as promotable resources (which need access to tools like crm_attribute) work seamlessly on the remote nodes.

Higher-level command shells such as pcs may have partial support on remote nodes, but it is recommended to run them from a cluster node.

4.7. Troubleshooting a Remote Connection

Note: This section should not be done when the remote is connected to the cluster.

Should connectivity issues occur, it can be worth verifying that the cluster nodes can contact the remote node on port 3121. Here’s a trick you can use. Connect using ssh from each of the cluster nodes. The connection will get destroyed, but how it is destroyed tells you whether it worked or not.

If running the ssh command on one of the cluster nodes results in this output before disconnecting, the connection works:

# ssh -p 3121 remote1
ssh_exchange_identification: read: Connection reset by peer

If you see one of these, the connection is not working:

# ssh -p 3121 remote1
ssh: connect to host remote1 port 3121: No route to host
# ssh -p 3121 remote1
ssh: connect to host remote1 port 3121: Connection refused

Once you can successfully connect to the remote node from the both cluster nodes, you may move on to setting up Pacemaker on the cluster nodes.