It's not uncommon in Pacemaker clusters to run specific cron jobs only
on a node that currently runs a particular resource. The
ocf:heartbeat:symlink resource agent can be exceptionally helpful in
this situation. Here's how to use it.
Suppose you've got a cron job for Postfix whose definition normally
/etc/cron.d/postfix. All your Postfix related data is in a
/srv/postfix (that filesystem could live on iSCSI, or DRBD,
or it could be a GlusterFS mount – that's irrelevant for the purposes
of this discussion). And as such, you've moved your cron definition to
Now you want that cron job to execute only on the node that also is currently the active Postfix host. That's not hard at all:
primitive p_postfix ocf:heartbeat:postfix \ params config_dir="/etc/postfix" \ op monitor interval="10" primitive p_symlink ocf:heartbeat:symlink \ params target="/srv/postfix/cron" \ link="/etc/cron.d/postfix" \ backup_suffix=".disabled" \ op monitor interval="10" primitive p_cron lsb:cron \ op monitor interval=10 order o_symlink_before_cron inf: p_symlink p_cron colocation c_cron_on_symlink inf: p_cron p_symlink colocation c_symlink_on_postfix inf: p_symlink p_postfix
What this will do for you is this:
Check whether a file named
postfixalready exists in
If it does, rename it to
postfix.disabled(remember, cron ignores job definitions with dots in the filename)
(Re-)Create the postfix job definition as a symlink to
cronwhen it's done.
c_symlink_on_postfix colocation ensures that all of this happens
on the node where the
p_postfix resource is also active.
This article originally appeared on the
hastexo.com website (now defunct).