[Pacemaker] pacemaker resource constraints

[Alan Jones]

Friends,
I have what should be a simple goal.  Two resources to run on two nodes.
I'd like to configure them to run on separate nodes when available, ie.
active-active,
and provide for them to run together on either node when one fails, ie.
failover.
Up until this point I have assumed that this would be a base use case for
Pacemaker, however, it seems from the discussion on:
http://wiki.lustre.org/index.php/Using_Pacemaker_with_Lustre
... that it is not (see below).  Any ideas?
Alan

*Note:* Use care when setting up your point system. You can use the
point system if your cluster has at least three nodes or if the resource
can acquire points from other constraints. However, in a system with
only two nodes and no way to acquire points, the constraint in the
example above will result in an inability to migrate a resource from a
failed node.

The example they refer to is similar to yours:

# crm configure colocation colresOST1resOST2 -100: resOST1 resOST2
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