[ClusterLabs] HA Cluster and Fencing

[Ken Gaillot]

On 09/03/2015 11:44 AM, Streeter, Michelle N wrote:
> I was trying to get a HA Cluster working but it was not failing over.   In past posts, someone kept asking me to get the fencing working and make it a priority.  So I finally got the fencing to work with VBox.  And the fail over finally started working for my HA cluster.   When I tried to explain this to my lead, he didn't believe me that the fencing was the issue with the fail over.   So, would someone help me understand why this happened so I can explain it to my lead.   Also, when I was trying to get Pacemaker 1.1.11 working, it was failing over fine without the fencing but when I added more than one drive to be serviced by the cluster via NFS.   The drives were being serviced by  both nodes almost as if it was load balancing.  It was suggested back then to get the fencing working.   So I take it if I went back to that version, this would have fixed the issue.  Would you also help me explain why this is true?
> 
> Michelle Streeter
> ASC2 MCS - SDE/ACL/SDL/EDL OKC Software Engineer
> The Boeing Company

Hi Michelle,

Congratulations on getting fencing working.

There's not enough information about your configuration to answer your
questions, but fencing is more a requirement for general cluster
stability rather than a solution to the specific problems you were facing.

Regarding load-balancing, I'm not sure whether you mean that a single
resource was started on multiple nodes, or different resources were
spread out on multiple nodes.

If one resource is active on multiple nodes, that means it was defined
as a clone or master-slave resource in your configuration. Clones are
used for active-active HA. If you want active-passive, where the
resource is only active on one node, don't clone it.

If instead you mean that multiple resources were spread out among nodes,
that's Pacemaker's default behavior. If you want two resources to always
be started together on the same node, you need to define a colocation
constraint for them (as well as an ordering constraint if one has to
start before the other), or put them in a resource group.