[ClusterLabs] Quorum With Two Nodes And an "observer" Questions

Digimer lists at alteeve.ca
Sat Sep 19 04:23:20 EDT 2015

On 18/09/15 03:32 AM, Ariel S wrote:
> Right now we are building a(nother) cluster, that basically built from two
> physical servers with VMs running resources managed by Pacemaker. Since
> this is
> two-node setup, and I'm constrained only to that two beefy servers, I
> realize
> that this would mean quorum=1 which also means no majority vote.
> The VMs have multiple cluster, eg. gateway cluster, infrastructure
> cluster and
> postgresql cluster.
> I'm thinking I could (probably) ask for another (weak) server which would
> function as an observer, a quorum-maker. Quorum should be possible with 2
> against 1, right? I think this is possible, by setting resources priority
> towards -infinity from going to that quorum-maker server which means
> resources
> should  run on those two beefy servers.
> I probably will have to run multiple instance of corosync and pacemaker,
> with
> different configuration and authkey files (for each cluster in the beefy
> servers) in a small-ish baremetal centos box.
> My question, is this actually feasible? Anyone have run into this
> situation and
> come up with such idea too? Got anything to share about this?
> Thank you

Feasible, sure. Needed? No.

Quorum is nice to have, but if you use a fence delay on a node and tell
corosync to use 'wait_for_all', then you're fine. All the clusters I've
built in the last 5~6 years have been 2-node only. You just need to be
sure you've got the fencing/stonith sorted out well.


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