Due to recent standardization within the cluster filesystem community, they make use of a common distributed lock manager which makes use of Corosync for its messaging capabilities and Pacemaker for its membership (which nodes are up/down) and fencing services.
Pacemaker本身由四个关键组件组成:
The CIB uses XML to represent both the cluster’s configuration and current state of all resources in the cluster. The contents of the CIB are automatically kept in sync across the entire cluster and are used by the PEngine to compute the ideal state of the cluster and how it should be achieved.
This list of instructions is then fed to the DC (Designated Co-ordinator). Pacemaker centralizes all cluster decision making by electing one of the CRMd instances to act as a master. Should the elected CRMd process, or the node it is on, fail… a new one is quickly established.
The DC carries out the PEngine’s instructions in the required order by passing them to either the LRMd (Local Resource Management daemon) or CRMd peers on other nodes via the cluster messaging infrastructure (which in turn passes them on to their LRMd process).
节点会把他们所有操作的日志发给DC，然后根据预期的结果和实际的结果(之间的差异)， 执行下一个等待中的命令，或者取消操作，并让PEngine根据非预期的结果重新计算集群的理想状态。
在某些情况下，可能会需要关闭节点的电源来保证共享数据的完整性或是完全地恢复资源。为此Pacemaker引入了STONITHd。STONITH是 Shoot-The-Other-Node-In-The-Head(爆其他节点的头)的缩写，并且通常是靠远程电源开关来实现的。在Pacemaker中，STONITH设备被当成资源(并且是在CIB中配置)从而轻松地监控，然而STONITHd会注意理解STONITH拓扑，比如它的客户端请求隔离一个节点，它会重启那个机器。(译者注:就是说不同的爆头设备驱动会对相同的请求有不同的理解，这些都是在驱动中定义的。)
