On Wed, Aug 9, 2017 at 5:01 AM, Miguel Angel Ajo Pelayo
<majop...@redhat.com> wrote:
> Nice idea, I have btw some comments/thoughts/questions regarding this:
> 1) Does OVSDB have any heartbeat protocol? (to detect that one northd has
> died even during inactive periods).

Yes, it does.  By deafult, both ends of an OVSDB connection send a
regular keepalive message every 5 seconds to help detect a dead
connection.  It's configurable, and the default has caused extra
reconnects when doing performance testing and services get too busy to
keep up with the default keepalive settings.

>      Otherwise we can document the need to tweak the tcp_keepalive settings
> of the system to have some sensible settings that will make TCP detect the
> connection failure in a reasonable amount of time.


> 2) We need to consider that in some cases the master ovsdb server and the
> northd process will be colocated and therefore fall together. I guess that
> in that case the lock is replicated to the slave ovsdb server, we need to
> make sure that the lock will be dropped once the old slave(backup) becomes
> master.

Good question.  I didn't look into how this behaves with
active/passive ovsdb-server.  I assume all locks are dropped when
services have to reconnect to the new master.  We should test it.

Also note that our Pacemaker config currently still manages
ovn-northd, so we're not exclusively relying on this behavior.  At a
minimum, if we still let Pacemaker drive the HA (because we're running
Pacemaker for ovsdb still anyway), this addition helps ensure that
only a single ovn-northd is active if somehow more than one was
accidentally started.
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