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---
layout: pacemaker
title: ClusterLabs - Components
---
<section id="main">
<a id="core"> </a>
<h1>Core Components</h1>
<h3><a href="/pacemaker.html">Pacemaker</a></h3>
<p>
At its core, Pacemaker is a distributed finite state
machine capable of co-ordinating the startup and recovery
of inter-related services across a set of machines.
</p>
<p>
Pacemaker understands many different resource types (OCF,
SYSV, systemd) and can accurately model the relationships
between them (colocation, ordering).
</p>
<p>
It can even use technology such
as <a href="https://www.docker.com">Docker</a> to
automatically isolate the resources managed by the
cluster.
</p>
<h3><a href="http://corosync.github.io/corosync/">Corosync</a></h3>
<p>
Corosync APIs provide membership (a list of peers),
messaging (the ability to talk to processes on those
peers), and quorum (do we have a majority) capabilities to
projects such as Apache Qpid and Pacemaker.
</p>
<h3><a href="http://clusterlabs.github.io/libqb/">libQB</a></h3>
<p>
libqb is a library with the primary purpose of providing
high performance client server reusable features. It
provides high performance logging, tracing, ipc, and poll.
</p>
<p>
The initial features of libqb come from the parts of
corosync that were thought to useful to other projects.
</p>
<h3><a href="https://github.com/ClusterLabs/resource-agents/">Resource Agents</a></h3>
<p>
Resource agents are the abstraction that allows Pacemaker
to manage services it knows nothing about. They contain
the logic for what to do when the cluster wishes to start,
stop or check the health of a service.
</p>
<p>
This particular set of agents conform to the Open Cluster
Framework (OCF) specification.
A <a href="https://github.com/ClusterLabs/resource-agents/blob/master/doc/dev-guides/ra-dev-guide.txt">guide
to writing agents</a> is also available.
</p>
<h3><a href="https://github.com/ClusterLabs/fence-agents/">Fence Agents</a></h3>
<p>
Fence agents are the abstraction that allows Pacemaker to
isolate badly behaving nodes. They achieve this by either
powering off the node or disabling its access to the
network and/or shared storage.
</p>
<p>
Many types of network power switches exist and you will
want to choose the one(s) that match your hardware.
Please be aware that some (ones that don't loose power
when the machine goes down) are better than others.
</p>
<p>
Agents are generally expected to expose OCF-compliant
metadata.
</p>
<h3><a href="https://github.com/ClusterLabs/OCF-spec/">OCF specification</a></h3>
<p>
The original documentation that sparked a lot of this
work. Mostly we only use the "RA" specification. Efforts
are underway to revive the process for updating and
modernizing the spec.
</p>
<a id="addons"> </a>
<h1>Configuration Tools</h1>
<p>
Pacemaker's internal configuration format is XML, which is
great for machines but terrible for humans.
</p>
<p>
The community's best minds have created GUIs and Shells to
hide the XML and allow the configuration to be viewed and
updated in a more human friendly format.
</p>
<h2>Command Line Interfaces (Shells)</h2>
<h3><a href="http://crmsh.github.io/">crmsh</a></h3>
<p>
The original configuration shell for Pacemaker. Written
and actively maintained by SUSE, it may be used either as an
interactive shell with tab completion, for single commands
directly on the shell's command line or as batch mode
scripting tool. Documentation for crmsh can be
found <a href="http://crmsh.github.io/documentation/">here</a>.
</p>
<h3><a href="https://github.com/feist/pcs">pcs</a></h3>
<p>
An alternate vision for a full cluster lifecycle
configuration shell and web based GUI. Handles everything
from cluster installation through to resource
configuration and status.
</p>
<h2>GUI Tools</h2>
<h3><a href="https://github.com/ClusterLabs/pacemaker-mgmt">pygui</a></h3>
<p>
The original GUI for Pacemaker written in Python by IBM
China. Mostly deprecated on SLES in favor of Hawk
</p>
<h3><a href="http://hawk-ui.github.io/">Hawk</a></h3>
<p>
Hawk is a web-based GUI for managing and monitoring
Pacemaker HA clusters. It is generally intended to be run
on every node in the cluster, so that you can just point
your web browser at any node to access it.
There is a usage guide at <a href="http://hawk-guide.readthedocs.org/en/latest/">hawk-guide.readthedocs.org</a>, and it is
documented as part of the
<a href="http://www.suse.com/documentation/sle_ha/book_sleha/?page=/documentation/sle_ha/book_sleha/data/cha_ha_configuration_hawk.html">
SUSE Linux Enterprise High Availability Extension documentation</a>
</p>
<h3><a href="http://lcmc.sf.net">LCMC</a></h3>
<p>
The Linux Cluster Management Console (LCMC) is a GUI with
an inovative approach for representing the status of and
relationships between cluster services. It uses SSH to
let you install, configure and manage clusters from your
desktop.
</p>
<h3><a href="https://github.com/feist/pcs">pcs</a></h3>
<p>
An alternate vision for a full cluster lifecycle
configuration shell and web based GUI. Handles everything
from cluster installation through to resource
configuration and status.
</p>
<h3><a href="https://github.com/ClusterLabs/striker">Striker</a></h3>
<p>
Striker is the user interface for the Anvil! (virtual) server
platform and the ScanCore autonomous self-defence and alert
system.
</p>
<h1>Other Add-ons</h1>
<h3><a href="https://github.com/ClusterLabs/booth">booth</a></h3>
<p>
The Booth cluster ticket manager extends Pacemaker to
support geographically distributed clustering. It does
this by managing the granting and revoking of 'tickets'
which authorizes one of the cluster sites, potentially
located in geographically dispersed locations, to run
certain resources.
</p>
<h3><a href="https://github.com/ClusterLabs/sbd">sbd</a></h3>
<p>
SBD provides a node fencing mechanism through the
exchange of messages via shared block storage such as for
example a SAN, iSCSI, FCoE. This isolates the fencing
mechanism from changes in firmware version or dependencies on
specific firmware controllers, and it can be used as a STONITH
mechanism in all configurations that have reliable shared
storage. It can also be used as a pure watchdog-based fencing
mechanism.
</p>
</section>

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