* Lukas Straub (lukasstra...@web.de) wrote: > On Fri, 16 Aug 2019 01:51:20 +0000 > "Zhang, Chen" <chen.zh...@intel.com> wrote: > > > > -----Original Message----- > > > From: Lukas Straub [mailto:lukasstra...@web.de] > > > Sent: Friday, August 16, 2019 3:48 AM > > > To: Dr. David Alan Gilbert <dgilb...@redhat.com> > > > Cc: qemu-devel <firstname.lastname@example.org>; Zhang, Chen > > > <chen.zh...@intel.com>; Jason Wang <jasow...@redhat.com>; Xie > > > Changlong <xiechanglon...@gmail.com>; Wen Congyang > > > <wencongya...@huawei.com> > > > Subject: Re: [Qemu-devel] [PATCH v2 0/3] colo: Add support for continious > > > replication > > > > > > On Thu, 15 Aug 2019 19:57:37 +0100 > > > "Dr. David Alan Gilbert" <dgilb...@redhat.com> wrote: > > > > > > > * Lukas Straub (lukasstra...@web.de) wrote: > > > > > Hello Everyone, > > > > > These Patches add support for continious replication to colo. > > > > > Please review. > > > > > > > > > > > > OK, for those who haven't followed COLO for so long; 'continuous > > > > replication' is when after the first primary fails, you can promote > > > > the original secondary to a new primary and start replicating again; > > > > > > > > i.e. current COLO gives you > > > > > > > > p<->s > > > > <primary fails> > > > > s > > > > > > > > with your patches you can do > > > > > > > > s becomes p2 > > > > p2<->s2 > > > > > > > > and you're back to being resilient again. > > > > > > > > Which is great; because that was always an important missing piece. > > > > > > > > Do you have some test scripts/setup for this - it would be great to > > > > automate some testing. > > > > > > My Plan is to write a Pacemaker Resource Agent for qemu-colo and then > > > do > > > some long-term testing in my small cluster here. Writing standalone tests > > > using > > > that Resource Agent should be easy, it just needs to be provided with the > > > right > > > arguments and environment Variables.
Could you update tests/test-replication.c to test the extra steps? Dave > > Thanks Dave's explanation. > > It looks good for me and I will test this series in my side. > > > > Another question: Is "Pacemaker Resource Agent " like a heartbeat > > module? > > It's a bit more than that. Pacemaker itself is an Cluster Resource Manager, > you can think of it like sysvinit but for clusters. It controls where in the > cluster Resources run, what state (master/slave) and what to do in case of a > Node or Resource failure. Now Resources can be anything like SQL-Server, > Webserver, VM, etc. and Pacemaker itself doesn't directly control them, > that's the Job of the Resource Agents. So a Resource Agent is like an > init-script, but cluster-aware with more actions like start, stop, monitor, > promote (to master) or migrate-to. > > > I have wrote an internal heartbeat module running on Qemu, it make COLO can > > detect fail and trigger failover automatically, no need external APP to > > call the QMP command "x-colo-lost-heartbeat". If you need it, I can send a > > RFC version recently. > > Cool, this should be faster to failover than with Pacemaker. > What is the plan with cases like Primary-failover, which need to issue > multiple commands? > > > Thanks > > Zhang Chen > > > > > > Regards, > > > Lukas Straub > > > > > >  > > > https://github.com/ClusterLabs/resource-agents/blob/master/doc/dev-guides/ra-dev-guide.asc#what-is-a-resource-agent > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK