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 does not include any capability of recovering from failure.
To make the control tier highly available, Pacemaker is added to the cluster to monitor services, filesystems, networking resources, and other resources that is it not sufficient to simply load-balance, they 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. Triple-O will install and configure a highly available control tier with the previously shown options passed to overcloud deploy in this chapter.
There are two major infrastructure considerations that go into designing a Pacemaker cluster. These points are related to the installation of Pacemaker and preparing it to start managing...