On Tue, Aug 1, 2017 at 5:00 AM, Han Zhou <zhou...@gmail.com> wrote:

> On Mon, Jul 31, 2017 at 1:53 PM, Russell Bryant <russ...@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.
> >
>

In the case of Pacemaker, the pacemaker OCF resource script
 (ovndb-servers.ocf) starts the ovn-northd on the master node if
manage_northd is set to true and this is the approach tripleo has taken.
ovn-northd uses the unix sockets to communicate to the NB and SB db servers.
With the suggested approach, ovn-northd would be using tcp connection to
communicate to the db servers ?

Thanks
Numan




> 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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