:compat-mode: legacy

= Troubleshooting Cluster Problems =

== Logging ==

Pacemaker by default logs messages of notice severity and higher to the system

log, and messages of info severity and higher to the detail log, which by

default is /var/log/pacemaker/pacemaker.log.

Logging options can be controlled via environment variables at Pacemaker

start-up. Where these are set varies by operating system (often

+/etc/sysconfig/pacemaker+ or +/etc/default/pacemaker+).

Because cluster problems are often highly complex, involving multiple machines,

cluster daemons, and managed services, Pacemaker logs rather verbosely to

provide as much context as possible. It is an ongoing priority to make these

logs more user-friendly, but by necessity there is a lot of obscure, low-level

information that can make them difficult to follow.

The default log rotation configuration shipped with Pacemaker (typically

installed in /etc/logrotate.d/pacemaker) rotates the log when it reaches 100MB

in size, or weekly, whichever comes first.

If you configure debug or (Heaven forbid) trace-level logging, the logs can

grow enormous quite quickly. Because rotated logs are by default named with the

year, month, and day only, this can cause name collisions if your logs exceed

100MB in a single day. You can add +dateformat -%Y%m%d-%H+ to the rotation

configuration to avoid this.

== Transitions ==

A key concept in understanding how a Pacemaker cluster functions is a

'transition'. A transition is a set of actions that need to be taken to bring

the cluster from its current state to the desired state (as expressed by the

configuration).

Whenever a relevant event happens (a node joining or leaving the cluster,

a resource failing, etc.), the controller will ask the scheduler to recalculate

the status of the cluster, which generates a new transition. The controller

then performs the actions in the transition in the proper order.

Each transition can be identified in the logs by a line like:

----

Nov 30 20:28:16 rhel7-1 pacemaker-schedulerd[36417] (process_pe_message)        notice: Calculated transition 19, saving inputs in /var/lib/pacemaker/pengine/pe-input-1463.bz2

----

The file listed as the "inputs" is a snapshot of the cluster configuration and

state at that moment (the CIB). This file can help determine why particular

actions were scheduled. The `crm_simulate` command, described in

<<s-crm_simulate>>, can be used to replay the file.

== Further Information About Troubleshooting ==

Andrew Beekhof wrote a series of articles about troubleshooting in his blog,

 http://blog.clusterlabs.org/[The Cluster Guy]:

* http://blog.clusterlabs.org/blog/2013/debugging-pacemaker[Debugging Pacemaker]

* http://blog.clusterlabs.org/blog/2013/debugging-pengine[Debugging the Policy Engine]

* http://blog.clusterlabs.org/blog/2013/pacemaker-logging[Pacemaker Logging]

The articles were written for an earlier version of Pacemaker, so many of the

specific names and log messages to look for have changed, but the concepts are

still valid.