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1.2. What Is Pacemaker?

Pacemaker is a high-availability cluster resource manager — software that runs on a set of hosts (a cluster of nodes) in order to preserve integrity and minimize downtime of desired services (resources). [4] It is maintained by the ClusterLabs community.
Pacemaker’s key features include:


Fencing, also known as STONITH (an acronym for Shoot The Other Node In The Head), is the ability to ensure that it is not possible for a node to be running a service. This is accomplished via fence devices such as intelligent power switches that cut power to the target, or intelligent network switches that cut the target’s access to the local network.
Pacemaker represents fence devices as a special class of resource.
A cluster cannot safely recover from certain failure conditions, such as an unresponsive node, without fencing.

[4] Cluster is sometimes used in other contexts to refer to hosts grouped together for other purposes, such as high-performance computing (HPC), but Pacemaker is not intended for those purposes.