On Tue, Jul 26, 2016 at 11:59 AM, Russell Bryant <russ...@ovn.org> wrote:
> > > On Tue, Jul 26, 2016 at 2:41 PM, Andy Zhou <az...@ovn.org> wrote: > >> >> >> On Tue, Jul 26, 2016 at 5:37 AM, Russell Bryant <russ...@ovn.org> wrote: >> >>> >>> >>> On Mon, Jul 25, 2016 at 8:15 PM, Andy Zhou <az...@ovn.org> wrote: >>> >>>> Hi, Rayn and Russell, >>>> >>> >>> Can we move this discussion to the ovs dev mailing list? Feel free to >>> just add it in a reply if you'd like. >>> >> Done. >> >>> >>> >>>> I am wondering how we can actually use the active/backup feature that >>>> is now part of >>>> OVSDB to increase OVN availability. >>>> >>> >>> TO be clear, I haven't actually tried this yet. I'm only speaking about >>> how I think it should work. >>> >>> >>>> Specifically: >>>> >>>> 1. When the active OVSDB server failed, should the back up server take >>>> over, and allow write transactions? One simpler possibility is to allow >>>> read only access to the backup serve. >>>> >>> >>> The backup server needs to take over. It's OK if that requires >>> intervention by an HA manager like Pacemaker. If we can't make the passive >>> server take over, I'd say the solution is incomplete. >>> >> >> O.K. make sense. >> >> One possible issue with backup server taking over is "split head". In >> case due to network error, backup server becomes disconnected from the >> active >> server, then we may have both server thinking they are active server >> now. Does Pacemaker help with solving this issue. >> > > It can, yes. I would expect Pacemaker to explicitly configure a node to > be either the active or passive node. > Manual switching is more straight forward. I agree. > >>> >>>> 2. When a crashed active OVSDB server recovers, should it become the >>>> new backup, or it should switch back. >>>> >>> >>> Becoming the new backup is fine. Again, this can be orchestrated by an >>> HA manager (Pacemaker). >>> >> I am not familiar with pacemaker. Can I assume it can provide a correct >> --sync-from argument (pointing to backup server) when relaunch OVSDB >> server? >> > > Yes. I'd have to consult with some Pacemaker experts on exactly what the > implementation would look like, but roughly: > > Pacemaker manages services using "OCF Resource Agents", which are just > scripts with a defined set of inputs and outputs for service management. I > would imagine a Pacemaker cluster being told it must have exactly 1 active > and 1 passive OVSDB service. When the passive OVSDB service is started, it > would include the "sync-from" argument based on where the active OVSDB > service is currently running. > > We really need to prototype this and document it. I'm guessing too much. > Pacemaker is frequently used to manage active/passive HA, though. > > Sounds reasonable, I will work on ovsdb internal changes to support manual switching, using appctl commands. Then looking into prototyping with HA systems. I have not used pacemaker in the past, so it may take some time to ramp up. > >>> >>>> Ben said one of you, or both may have worked with similar active-backup >>>> systems before, so I am very interested in your inputs. >>>> >>>> Thanks, >>>> >>>> Andy >>>> >>> >>> >>> >>> -- >>> Russell Bryant >>> >> >> > -- > Russell Bryant > _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
