[ClusterLabs] Resource clone groups - resource deletion

Adrian Saul Adrian.Saul at tpgtelecom.com.au
Tue May 10 04:06:15 EDT 2016

 I am building up a service for doing ALUA based iSCSI targets using pacemaker for configuration management and failover of target groups.   This is done using our own developed resource scripts.
To keep the config clean I have organised resources into groups - as I create resources they are added to the groups, and the groups are either clone or master groups to apply the configuration across the cluster:

devicegroups -  master/slave group for controlling the ALUA states
targets - iSCSI targets - clone group
devices - iSCSI backing devices - clone group
hostgroups - iSCSI hostgroups and LUN mappings - clone group

There are constraints that order the devicegroup groups then targets.  Targets then hostgroups and devices then hostgroups.  I have enabled interleaving as well.

This works reasonably well with two issues.  The first is that a configuration error in one resource can take down the entire group rather than just the faulty resource - for example a typo in the attributes for a device resource pointing to a non-existing device can cause it to error, taking down the device group and by order constraints the hostgroups too.  This makes a small mistake a big one as devices go offline unnecessarily.

The second is that it appears deleting a resource from the group (using pcs resource delete) causes the policy engine to stop the entire group and dependencies, remove the resource, then start them all again - which is very disruptive to iSCSI traffic.   For example if I remove a device that is no longer in use by a hostgroup, it triggers a stop of the devices and hostgroups groups, removes the device, then starts them all again.

Is there a way I can avoid these two behaviours maintaining this simpler group level config, or am I simply using them the wrong way?

The alternative I am guessing would be to make each resource its own clone instead, and do individual resource constraints more finely rather than wholesale group constraints, which is possible but would require some more careful configuration management to ensure constraints and resources are properly associated.



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