[ClusterLabs] Prevent cluster transition when resource unavailable on both nodes

[Alexander Eastwood]

Hello, 

I administrate a Pacemaker cluster consisting of 2 nodes, which are connected to each other via ethernet cable to ensure that they are always able to communicate with each other. A network switch is also connected to each node via ethernet cable and provides external access.

One of the managed resources of the cluster is a virtual IP, which is assigned to a physical network interface card and thus depends on the network switch being available. The virtual IP is always hosted on the active node.

We had the situation where the network switch lost power or was rebooted, as a result both servers reported `NIC Link is Down`. The recover operation on the Virtual IP resource then failed repeatedly on the active node, and a transition was initiated. Since the other node was also unable to start the resource, the cluster was swaying between the 2 nodes until the NIC links were up again.

Is there a way to change this behaviour? I am thinking of the following sequence of events, but have not been able to find a way to configure this:

 1. active node detects NIC Link is Down, which affects a resource managed by the cluster (monitor operation on the resource starts to fail)
 2. active node checks if the other (passive) node in the cluster would be able to start the resource
 3. if passive node can start the resource, transition all resources to passive node
 4. if passive node is unable to start the resource, then there is nothing to be gained a transition, so no action should be taken

Any pointers or advice will be much appreciated!

Thank you and kind regards,

Alex Eastwood