Cluster Membership

There are three levels of cluster[1] membership, each one allowing different actions and each requiring the one before it.

The first and lowest is that provided by Heartbeat[2]. This level allows messages to be sent to other nodes[3] on the network also running Heartbeat and provides notification of other ClusterNodes[4] coming up or going down. In its current incarnation, this level also allows you to perform ResourceAllocation[5] between two ClusterNodes[4], this will no longer be the case once the new ClusterResourceManager[6] is mandatory.

The next level is that provided by the ClusterConsensusManager[7]. This level provides interested parties with a list of FullyConnected[8] ClusterNodes[4] by subscribing to the node-up, node-down events from Heartbeat and by also using it as a reliable messaging layer to send "ping" messages to other ClusterNodes[4] as well as other wonderful things I'll come back to one day.

The third is provided by ClusterResourceManager[6]. This level allows ResourceAllocation[5] across N ClusterNodes[4]. It utilizes the list of FullyConnected[8] ClusterNodes[4] provided by the ClusterConsensusManager[7] to elect a DesignatedController[9].

---

This information provided courtesy of the Linux-HA project at http://linux-ha.org/