[ClusterLabs] pacemaker geo redundancy - 2 nodes

Ken Gaillot kgaillot at redhat.com
Mon Jul 15 15:57:09 EDT 2019

On Mon, 2019-07-15 at 12:10 +0530, Rohit Saini wrote:
> Hi All,
> I know pacemaker booth is being used for geographical redundancy.
> Currently I am using pacemaker/corosync for my local two-node
> redundancy.
> As I understand, booth needs atleast 3 nodes to work correctly to do
> the automatic failovers. So it does not fit my requirements.

Booth needs a third site, but it doesn't need to be a cluster node. It
can be a lightweight host running just the booth arbitrator.

However you do need full clusters at each site, so at least two nodes
at each site, plus the arbitrator host.

> Few queries are
> 1) Can I make use of my current pacemaker/corosync to make it work
> across my two geographical nodes for automatic failovers, considering
> I am ready to ignore split-brain scenarios. I may need to tweak some
> timers I believe. Is this approach possible?

Yes, this is sometimes referred to as a "stretched" or "metro" cluster.
You can raise the corosync token timeout as needed to cover typical
latencies. However this is generally only recommended when the
connection between the two sites is highly reliable and low latency.

A lightweight host at a third site running qdevice can be used to
provide true quorum.

> 2) Any disadvantages of going this way?

Raising the token timeout will delay the response to actual
node/network failures by the same amount.

If you're thinking of doing it without fencing, the consequences of
split brain depend on your workload. Something like a database or
cluster filesystem could become horribly corrupted.

> Thanks,
> Rohit
Ken Gaillot <kgaillot at redhat.com>

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