[ClusterLabs] Is fencing really a must for Postgres failover?

[Maciej S]

Thank you all for the answers. I can see your point, but anyway it seems
that fencing is like for additional precaution.
If my requirements allow some manual intervention in some cases (eg.
unknown resource state after failover), then I might go ahead without
fencing. At least until STONITH is not mandatory :)

Thanks,
Maciej


pon., 11 lut 2019 o 17:54 Digimer <lists at alteeve.ca> napisał(a):

> On 2019-02-11 6:34 a.m., Maciej S wrote:
> > I was wondering if anyone can give a plain answer if fencing is really
> > needed in case there are no shared resources being used (as far as I
> > define shared resource).
> >
> > We want to use PAF or other Postgres (with replicated data files on the
> > local drives) failover agent together with Corosync, Pacemaker and
> > virtual IP resource and I am wondering if there is a need for fencing
> > (which is very close bind to an infrastructure) if a Pacemaker is
> > already controlling resources state. I know that in failover case there
> > might be a need to add functionality to recover master that entered
> > dirty shutdown state (eg. in case of power outage), but I can't see any
> > case where fencing is really necessary. Am I wrong?
> >
> > I was looking for a strict answer but I couldn't find one...
> >
> > Regards,
> > Maciej
>
> Fencing is as required as a wearing a seat belt in a car. You can
> physically make things work, but the first time you're "in an accident",
> you're screwed.
>
> Think of it this way;
>
> If services can run in two or more places at the same time without
> coordination, you don't need a cluster, just run things everywhere. If
> you need coordination though, you need fencing.
>
> The role of fencing is to force a node that has entered into an unknown
> state and force it into a known state. In a system that requires
> coordination, often times fencing is the only way to ensure sane operation.
>
> Also, with pacemaker v2, fencing (stonith) became mandatory at a
> programmatic level.
>
> --
> Digimer
> Papers and Projects: https://alteeve.com/w/
> "I am, somehow, less interested in the weight and convolutions of
> Einstein’s brain than in the near certainty that people of equal talent
> have lived and died in cotton fields and sweatshops." - Stephen Jay Gould
>
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