Version 1 of Heartbeat came with its own style of resource agents and it is highly likely that many people have written their own agents based on its conventions. To enable administrators to continue to use these agents, they are supported by the new cluster manager.

For more information, see: http://wiki.linux-ha.org/HeartbeatResourceAgent

The OCF class is the most preferred one as it is an industry standard, highly flexible (allowing parameters to be passed to agents in a non-positional manner) and self-describing.

There is also an additional class, STONITH, which is used exclusively for fencing related resources. This is discussed later in Chapter 11, Protecting Your Data - STONITH.