Understanding Linux-HA

The Linux-HA stack is built from a set of modular components that provide services. The major parts of this stack are the messaging layer (Corosync), the cluster manager (Pacemaker), application adaptor scripts (resource agents), fencing adaptors for STONITH (fence agents), and command-line tools for configuring all of this (pcs). The details on how this stack is put together have varied over time and across distributions, so if you are using an older distribution, you might have some differences compared to what is being described here. For newer distributions, the digital world seems to be stabilizing and you shouldn't have major differences.

Corosync

The Corosync messaging layer is responsible for knowing which nodes are up and part of the clusters, handling reliable communications between nodes, and storing the cluster state in a reliable and consistent in-memory database.

Corosync uses a shared key for communications, which you need to generate when setting up your...