[ovs-dev] [RFC] Basic active-active HA for ovn-northd

Han Zhou zhouhan at gmail.com
Mon Jul 31 23:30:31 UTC 2017


On Mon, Jul 31, 2017 at 1:53 PM, Russell Bryant <russell at ovn.org> wrote:
>
> I wanted to share the idea before I code it to see if it makes sense.
> I imagine the patch would be small, though.
>
> We currently provide HA for ovn-northd by using Pacemaker to ensure
> that ovn-northd is running only one time somewhere in a cluster.
>
> What if we made ovn-northd acquire an OVSDB lock on the southbound
> database before it did any real work?  That way we could start
> multiple copies of ovn-northd in a cluster, but only one would be
> active at a time.
>
> This is crude, and obviously we would want to distribute work among
> ovn-northd instances eventually, but does this sound like an
> improvement over requiring something like Pacemaker?
>
Russell, this sounds very good. I think it is better than Pacemaker. I
would still call it active-standby though. The standby is hot-standby, not
cold-standby.

It seems the change would be having the active one updating <timestamp,
northd hostname> periodically to southbound DB, so that other northd will
know if it is still alive, and otherwise taking over by updating the
<timestamp, northd hostname>. Is this correct?


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