5.2. Monitor a Cluster with crm

⁠5.2. Monitor a Cluster with crm_mon

The crm_mon utility displays the current state of an active cluster. It can show the cluster status organized by node or by resource, and can be used in either single-shot or dynamically updating mode. It can also display operations performed and information about failures.

Using this tool, you can examine the state of the cluster for irregularities, and see how it responds when you cause or simulate failures.

See the manual page or the output of crm_mon --help for a full description of its many options.

⁠

Example 5.1. Sample output from crm_mon -1

Cluster Summary:
  * Stack: corosync
  * Current DC: node2 (version 2.0.0-1) - partition with quorum
  * Last updated: Mon Jan 29 12:18:42 2018
  * Last change:  Mon Jan 29 12:18:40 2018 by root via crm_attribute    on node3
  * 5 nodes configured
  * 2 resources configured

Node List:
  * Online: [ node1 node2 node3 node4 node5 ]

* Active resources:
  * Fencing (stonith:fence_xvm):    Started node1
  * IP  (ocf:heartbeat:IPaddr2):        Started node2

⁠

Example 5.2. Sample output from crm_mon -n -1

Cluster Summary:
  * Stack: corosync
  * Current DC: node2 (version 2.0.0-1) - partition with quorum
  * Last updated: Mon Jan 29 12:21:48 2018
  * Last change:  Mon Jan 29 12:18:40 2018 by root via crm_attribute    on node3
  * 5 nodes configured
  * 2 resources configured

* Node List:
  * Node node1: online
    * Fencing (stonith:fence_xvm):    Started
  * Node node2: online
    * IP        (ocf:heartbeat:IPaddr2):        Started
  * Node node3: online
  * Node node4: online
  * Node node5: online

As mentioned in an earlier section, the DC is the node is where decisions are made. The cluster elects a node to be DC as needed. The only significance of the choice of DC to an administrator is the fact that its logs will have the most information about why decisions were made.

⁠5.2.1. Styling crm_mon output

Various parts of crm_mon's HTML output have a CSS class associated with them. Not everything does, but some of the most interesting portions do. In the following example, the status of each node has an "online" class and the details of each resource have an "rsc-ok" class.

<h2>Node List</h2>
<ul>
<li>
<span>Node: cluster01</span><span class="online"> online</span>
</li>
<li><ul><li><span class="rsc-ok">ping   (ocf::pacemaker:ping):   Started</span></li></ul></li>
<li>
<span>Node: cluster02</span><span class="online"> online</span>
</li>
<li><ul><li><span class="rsc-ok">ping   (ocf::pacemaker:ping):   Started</span></li></ul></li>
</ul>

By default, a stylesheet for styling these classes is included in the head of the HTML output. The relevant portions of this stylesheet that would be used in the above example is:

<style>
.online { color: green }
.rsc-ok { color: green }
</style>

If you want to override some or all of the styling, simply create your own stylesheet, place it on a web server, and pass --html-stylesheet=<URL> to crm_mon. The link is added after the default stylesheet, so your changes take precedence. You don’t need to duplicate the entire default. Only include what you want to change.