[Pacemaker] Two-node cluster fencing

[Digimer]

On 21/10/13 10:18, Digimer wrote:
> 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
> 

Woops, s/Lars/Michael/. :)

-- 
Digimer
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