Pacemaker release version: This version consists of three numbers (x.y.z).
The major version number (the x in x.y.z) increases when at least some rolling upgrades are not possible from the previous major version. For example, a rolling upgrade from 1.0.8 to 1.1.15 should always be supported, but a rolling upgrade from 1.0.8 to 2.0.0 may not be possible.
The minor version (the y in x.y.z) increases when there are significant changes in cluster default behavior, tool behavior, and/or the API interface (for software that utilizes Pacemaker libraries). The main benefit is to alert you to pay closer attention to the release notes, to see if you might be affected.
The release counter (the z in x.y.z) is increased with all public releases of Pacemaker, which typically include both bug fixes and new features.
CRM feature set: This version number applies to the communication between full cluster nodes, and is used to avoid problems in mixed-version clusters.
The major version number increases when nodes with different versions would not work (rolling upgrades are not allowed). The minor version number increases when mixed-version clusters are allowed only during rolling upgrades. The minor-minor version number is ignored, but allows resource agents 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.
Pacemaker Remote protocol version: This version applies to communication between a Pacemaker Remote node and the cluster. It increases when an older cluster node would have problems hosting the connection to a newer Pacemaker Remote node. To avoid these problems, Pacemaker Remote nodes will accept connections only from cluster nodes with the same or newer Pacemaker Remote protocol version.
Unlike with CRM feature set differences between full cluster nodes, mixed Pacemaker Remote protocol versions between Pacemaker Remote nodes and full cluster nodes are fine, as long as the Pacemaker Remote nodes have the older version. This can be useful, for example, to host a legacy application in an older operating system version used as a Pacemaker Remote node.
XML schema version: Pacemaker’s configuration syntax — what’s allowed in the Configuration Information Base (CIB) — has its own version. This allows the configuration syntax to evolve over time while still allowing clusters with older configurations to work without change.
