[ClusterLabs] how to fence in a two node cluster.If haretbeat network is down between the two nodes, which node will fence the other node?

[Digimer]

On 05/11/15 02:09 AM, Shilu wrote:
> cid:image002.png at 01D1091A.AEFC8740
> 
> In HA, if a node is declared dead, it needs to be fenced/stonith'ed
> before its services are recovered. Not doing this can lead to a split-brain.
> 
> If haretbeat network is down between the two nodes,which node will fence
> the other node?
> 
> If two nodes were fenced respectively,the service will be not available.
> 
> I want to know if IPMI fence is appropriate to two nodes cluster. Is
> there a better fence way?

You will choose a node to be the survivor in this case, and the set
'delay="15"' in the IPMI fence attribute list.

If you set the delay against node 1, for example, then in a comm break
like you describe, both will declare the other dead and start fencing at
the same time. Node 1 looks up how to fence node 2, sees no delay and
immediately starts to fence. Meanwhile, node 2 looks up how to fence
node 1, sees a delay and pauses for 15 seconds. Node 1 will kill node 2
long before the delay expires.

Also, disable acpid. You want the node to react to the power button
being pressed by shutting down immediately.

Also, this doesn't solve all problems. Pull all power to a node. This
will cause IPMI to fail, so the fence call will fail. This is why I use
IPMI *and* a pair of switched PDUs (IPMI on one switch, PDUs on another).

-- 
Digimer
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