[ClusterLabs] what does cluster do when 'resourceA with resourceB' happens

[Ken Gaillot]

On Tue, 2017-10-03 at 11:53 +0100, lejeczek wrote:
> hi
> 
> I'm reading "An A-Z guide to Pacemaker's Configurations 
> Options" and in there it read:
> "...
> So when you are creating colocation constraints, it is 
> important to consider whether you should
> colocate A with B, or B with A.
> Another thing to keep in mind is that, assuming A is 
> colocated with B, the cluster will take into account
> A’s preferences when deciding which node to choose for B.
> ..."
> 
> I have a healthy cluster, three nodes, a five resources at 
> given time running on node1.
> Then I create a LVM resource which cluster decides to put on 
> node2.
> Then I do:
> 
> $ pcs constraint colocation add resourceA(running at node1) 
> with aLocalStorage6(newly created, running at node2)
> 
> I cluster moves all the resources to node2.
> 
> And I say whaaat? Something, guide+reality, does not ad up, 
> right?

That colocation constraint says "place aLocalStorage6 somewhere, then
place resourceA with it", so it makes sense resourceA moves there.

If everything else moves there, too, there must be something else in
the configuration telling it to. (Other colocation constraints maybe?)