1.4. Architettura di Pacemaker

Al livello più elevato il cluster è composto da tre componenti:

Infrastruttura core del cluster che rende disponibili le funzionalità di messaging e membership (illustrate in rosso)
Non-cluster aware components (illustrated in green).
In a Pacemaker cluster, these pieces include not only the scripts that knows how to start, stop and monitor resources, but also a local daemon that masks the differences between the different standards these scripts implement.
A brain (illustrated in blue)
This component processes and reacts to events from the cluster (nodes leaving or joining) and resources (eg. monitor failures) as well as configuration changes from the administrator. In response to all of these events, Pacemaker will compute the ideal state of the cluster and plot a path to achieve it. This may include moving resources, stopping nodes and even forcing nodes offline with remote power switches.

1.4.1. Panoramica concettuale dello Stack

Conceptual overview of the cluster stack

Figura 1.4. Panoramica concettuale dello stack del cluster

When combined with Corosync, Pacemaker also supports popular open source cluster filesystems. footnote:[ Even though Pacemaker also supports Heartbeat, the filesystems need to use the stack for messaging and membership and Corosync seems to be what they’re standardizing on.

Technically it would be possible for them to support Heartbeat as well, however there seems little interest in this. ]

Due to recent standardization within the cluster filesystem community, they make use of a common distributed lock manager which makes use of Corosync for its messaging capabilities and Pacemaker for its membership (which nodes are up/down) and fencing services.

The Pacemaker stack when running on Corosync

Figura 1.5. Lo stack Pacemaker nell'esecuzione su Corosync