Pacemaker feature set

Besides a release version, Pacemaker has a separate "CRM feature set". This version number applies to the communication between cluster nodes, and is used to avoid problems in mixed-version clusters.

Most of the time, CRM feature sets are for Pacemaker's internal use. However, they can also be used by resource agents and other external code to detect support for various features. The table below lists those features.

How CRM feature sets are numbered
The major version increases when nodes with different versions would not work together. Rolling upgrades would not be possible in this case.

The minor version increases when mixed-version clusters are allowed only during rolling upgrades. If one of the older nodes drops out of the cluster for any reason, it will not be able to rejoin until it is upgraded. In this case, you should run a mixed-version cluster only during a small upgrade window.

The minor-minor version number is ignored by Pacemaker. Clusters with different versions should work without problems. This number allows resource agents and other external code to detect cluster support for various features.

Pacemaker ensures that the longest-running node is the cluster’s DC. This ensures new features are not enabled until all nodes are upgraded to support them.