[Pacemaker] Two-node cluster fencing

[Digimer]

On 21/10/13 04:28, Timm Bordeman wrote:
> Hi,
> 
> I'm building a two-node cluster based on XenServer, Pacemaker and DRBD. All needed resources are configured and correctly handled by pacemaker, but currently I'm struggling with stonith / fencing.
> 
> Both physical servers are running XenServer and a couple of virtual machines which are being mirrored. For example, on each servers is an Apache-VM running which share a data partition over DRBD. I configured fencing over XEN, which is restarting any faulty VM reliable, as long as both physical servers are working correctly.
> 
> Unfortunately fencing doesn't work when a server that hosts a faulty virtual machine is powered off or not reachable over the network. In this case pacemaker does not promote the DRBD partition on the second / passive virtual machine to the primary partition. Other resources, like the apache server, won't get started. I know that this is an expected behaviour of Pacemaker and DRBD, but I'm not sure what is needed to make the failover reliable even in the case of a completely broken physical server. Fencing by issuing a reboot of the broken server obviously is not an option since the server wouldn't come up due to a hardware defect.
> 
> I appreciate any help on this.
> 
> Thanks,
> Tim

What fence agent(s) are you trying to use? Proper fencing works
regardless of what state or condition the target node is in. Can you
share your cluster's configuration?

Also, Lars is correct. You need to disable quorum on 2-node clusters.
This is fine because fencing prevents split-brain conditions, but it
does introduce some configuration issues. Most notably, you want to make
sure that pacemaker does not start on boot. If the network link between
the nodes fails, you can end up in a "fence loop" where the first node
to be fenced boots, starts pacemaker, fails to connect to it's peer and
fences it.

Cheers

-- 
Digimer
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