Re: [Qemu-devel] [PATCH v2 0/3] colo: Add support for continious replication

["Zhang, Chen" <chen.zhang@intel.com>]

> -----Original Message-----
> From: Lukas Straub [mailto:lukasstraub2@web.de]
> Sent: Friday, August 16, 2019 3:48 AM
> To: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Cc: qemu-devel <qemu-devel@nongnu.org>; Zhang, Chen
> <chen.zhang@intel.com>; Jason Wang <jasowang@redhat.com>; Xie
> Changlong <xiechanglong.d@gmail.com>; Wen Congyang
> <wencongyang2@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" <dgilbert@redhat.com> wrote:
> 
> > * Lukas Straub (lukasstraub2@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[1] 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.

Thanks Dave's explanation.
It looks good for me and I will test this series in my side.

Another question: Is "Pacemaker Resource Agent[1] "  like a heartbeat module?   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.

Thanks
Zhang Chen
> 
> Regards,
> Lukas Straub
> 
> [1] https://github.com/ClusterLabs/resource-agents/blob/master/doc/dev-
> guides/ra-dev-guide.asc#what-is-a-resource-agent