[ClusterLabs] Feedback wanted: Node reaction to fabric fencing

Jan Pokorný jpokorny at redhat.com
Thu Jul 25 08:22:28 EDT 2019

On 24/07/19 12:33 -0500, Ken Gaillot wrote:
> A recent bugfix (clbz#5386) brings up a question.
> A node may receive notification of its own fencing when fencing is
> misconfigured (for example, an APC switch with the wrong plug number)
> or when fabric fencing is used that doesn't cut the cluster network
> (for example, fence_scsi).

One related idea that'd be better to think through on its own pace,
whether it would make sense to maximize the benefit of knowing
which kind of behaviour to expect from particular abstracted
fencing device.  Is it absolute cut-off of the whole node's acting,
or is it just a partial isolation where it presumably matters
the most (access to disk, access to network resources, ...)?
Then, a dichotomy in failure modes could be introduced, since
these are effectively _different_ disaster limiting scenarios
with different pros and cons (consider also debug-ability).
I always had mixed feelings about putting total/partial fencing
into the same bucket.  Apparently, that information would need
to be propagated via the metadata of the agents, meaning pulling
more complexity on that level.

Broader picture might even be that compositions of the resources
could as well point out which kinds of shared resources are in
danger of amplifying the failure/causing split brain etc. and
hence offer the feedback which of these are yet to be covered
if the absolute cut-off is not preferred/available for whatever

/me gets back from daydreaming

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