Quorum – scoring inside your cluster

In simple terms, the concept of quorum indicates the minimum number of members that are required to be active in order for the cluster, as a whole, to be available. Specifically, a cluster is said to have quorum when the number of active nodes is greater than the total number of nodes divided by two. Another way to express this is that quorum is achieved by at least a simple majority (50% of the total number of nodes + 1).

Although the concept of quorum doesn't prevent a split-brain scenario, it will decide which node (or group of nodes) is dominant and allowed to run the cluster so that when a split-brain situation occurs, only one node (or group of nodes) will be able to run the cluster services.

By default, when the cluster does not have quorum, pacemaker will stop all resources altogether so that they will not be started on more nodes than desired. However, a cluster member will still listen for other nodes to reappear on the network, but they will...