[Pacemaker] Multi-node resource dependency

[Lars Ellenberg]

On Fri, Jul 19, 2013 at 04:49:21PM +0200, "Tomcsányi, Domonkos" wrote:
> Hello everyone,
> 
> I have been struggling with this issue for quite some time so I
> decided to ask you to see if maybe you can shed some light on this
> problem.
> So here is the deal:
> I have a 4-node cluster, from which 2-2 nodes belong together.
> In ASCII art it would look like this:
> 
> --------------         --------------
> | NODE1 |    --   | NODE 2  |
> --------------         --------------
> |                         |
> |                         |
> |                         |
> --------------         --------------
> | NODE 3 |  --  | NODE 4 |
> --------------         --------------
> 
> Now the behaviour I would like to achieve:
> If NODE 1 goes offline its services should get migrated to NODE 2
> AND NODE 3's services should get migrated to NODE 4.
> If NODE 3 goes offline its services should get migrated to NODE4 AND
> NODE1's services should get migrated to NODE 2.
> Of course the same should happen vice versa with NODE 2 and NODE 4.
> 
> The services NODE1 and 2 are the same naturally, but they differ
> from NODE 3's and 4's services. So I added some 'location'
> directives to the config so the services can only be started on the
> right nodes.
> I tried 'colocation' which is great, but not for this kind of
> behaviour: if I colocate both resource groups of NODE 1 and 3 only
> one of them starts (of course, because colocation means the
> resource/resource group(s) should be running on the same NODE, so my
> location directives kick in and prevent for example NODE 3's
> services from starting on NODE 1).
> 
> So my question is: is it possible to define such behaviour I
> described above in Pacemaker? If yes, how?

You may use node attributes in colocation constraints.

So you would give your nodes attributes, first:

crm node
	attribute NODE1 set color pink
	attribute NODE3 set color pink

	attribute NODE2 set color slime
	attribute NODE4 set color slime

crm configure
	colocation c-by-color inf: rsc_a rsc_b rsc_c node-attribute=color

The "implicit default" node-attribute is #uname ...
so using "color" the resources only need to run on nodes with the same
value for the node-attribute "color".

	Lars

-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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