Description:

heartbeat is a basic high-availability subsystem for Linux-HA.
It will run scripts at initialization, and when machines go up or down.
This version will also perform IP address takeover using gratuitous ARPs.

Heartbeat contains a cluster membership layer, fencing, and local and
clusterwide resource management functionality.

When used with Pacemaker, it supports "n-node" clusters with significant
capabilities for managing resources and dependencies.

In addition it continues to support the older release 1 style of
2-node clustering.

It implements the following kinds of heartbeats:
- Serial ports
- UDP/IP multicast (ethernet, etc)
- UDP/IP broadcast (ethernet, etc)
- UDP/IP heartbeats
- "ping" heartbeats (for routers, switches, etc.)
(to be used for breaking ties in 2-node systems)