Quorum in a two-node cluster

You learned about quorum in Chapter 2, Meet the Cluster Stack on CentOS. Quorum is the minimum number of cluster member votes required to perform a cluster operation. Without Quorum, the cluster cannot operate. Quorum is achieved when the majority of cluster members vote to execute a specific cluster operation. If no majority is reached, the cluster operation will not be performed.

You probably see where this is going. In a two-node cluster configuration, the maximum number of expected votes is two—each cluster node has one vote. In a cluster node failure scenario, only one cluster node is active and a cluster node has only one vote. In such a configuration, Quorum cannot be reached because no majority can be delivered. The single cluster node is stuck at 50 percent and will never get past that value. Therefore, the cluster will never operate normally in this way.

The quorum provider in the CentOS 7 cluster stack is Corosync. The CentOS 7 cluster stack, as opposed...