[Pacemaker] Using "avoids" location constraint

[Andrew Beekhof]

On 08/07/2013, at 11:35 PM, Andrew Morgan <andrewjamesmorgan at gmail.com> wrote:

> Thanks Florian.
> 
> The problem I have is that I'd like to define a HA configuration that isn't dependent on a specific set of fencing hardware (or any fencing hardware at all for that matter) and as the stack has the quorum capability included I'm hoping that this is an option.
> 
> I've not been able to find any quorum commands within pcs; the closest I've found is setting a node to "standby" but when I do that, it appears to have lost its quorum vote

This is not the case.

> - this seems at odds with the help text....
> 
> standby <node>
>         Put specified node into standby mode (the node specified will no longer be able to host resources
> 
> Regards, Andrew.
> 
> 
> On 8 July 2013 10:23, Florian Crouzat <gentoo at floriancrouzat.net> wrote:
> Le 08/07/2013 09:49, Andrew Morgan a écrit :
> 
> I'm attempting to implement a 3 node cluster where only 2 nodes are
> there to actually run the services and the 3rd is there to form a quorum
> (so that the cluster stays up when one of the 2 'workload' nodes fails).
> 
> To this end, I added a location avoids contraint so that the services
> (including drbd) don't get placed on the 3rd node (drbd3)...
> 
> pcs constraint location ms_drbd avoids drbd3.localdomain
> 
> the problem is that this constraint doesn't appear to be enforced and I
> see failed actions where Pacemaker has attempted to start the services
> on drbd3. In most cases I can just ignore the error but if I attempt to
> migrate the services using "pcs move" then it causes a fatal startup
> loop for drbd. If I migrate by adding an extra location contraint
> preferring the other workload node then I can migrate ok.
> 
> I'm using Oracle Linux 6.4; drbd83-utils 8.3.11; corosync 1.4.1; cman
> 3.0.12.1; Pacemaker 1.1.8 & pcs 1.1.8
> 
> 
> I'm no quorum-node expert but I believe your initial design isn't optimal.
> You could probably even run with only two nodes (real nodes) and no-quorum-policy=ignore + fencing (for data integrity) [1]
> This is what most (all?) people with two nodes clusters do.
> 
> But if you really believe you need to be quorate, then I think you need to define your third node as quorum-node in corosync/cman (not sure how since EL6.4 and CMAN) and I cannot find a valid link. IIRC with such definition, you won't need the location constraints.
> 
> 
> [1] http://clusterlabs.org/doc/en-US/Pacemaker/1.1-plugin/html/Clusters_from_Scratch/_perform_a_failover.html#_quorum_and_two_node_clusters
> 
> 
> 
> -- 
> Cheers,
> Florian Crouzat
> 
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