High availability

Until now, the architecture discussed has added additional instances of services and balanced traffic across them. While HAProxy has monitors built into it to check the health of a host, this is only to know whether or not to send traffic to the host. It doesn't include any capability of recovering from failure.

To make the control and network tiers highly available, Pacemaker can be added to the cluster to monitor services, file systems, networking resources, and other resources that need to be made highly available. Pacemaker is capable of moving services from node to node in a pacemaker cluster and monitoring the nodes to know whether action needs to be taken to recover a particular resource or even one of the entire nodes.

The installation and configuration of Pacemaker is a whole book in itself; here, we will just touch upon some of the major, important items to consider when configuring Pacemaker and the concept behind how it will handle some of our resources and what...