Pacemaker keeps your applications running when they or the machines they’re running on fail. However it can’t do this without connectivity to the other machines in the cluster – a significant problem in its own right.
Rather than re-implement the wheel, Pacemaker supports existing implimentations such as Heartbeat. Heartbeat provides:
- a mechansigm to reliably send messages between nodes,
- notifications when machines appear and disappear
- a list of machines that are up that is consistent throughout the cluster
Heartbeat was also the first stack supported by the Pacemaker codebase.
via FAQ – ClusterLabs.