[ClusterLabs] Q: callback hooks for sbd?

[Strahil Nikolov]

What about creating a custom fencing agent that does what you need and always reporting that it failed ?
Using fencing topology and a custom fencing script as the first stonith device (that always fails) , you will be able to execute some commands (or at least try to do that) before the next fencing mechanism kicks in.


Best Regards,
Strahil Nikolov






В четвъртък, 11 март 2021 г., 19:16:04 ч. Гринуич+2, Klaus Wenninger <kwenning at redhat.com> написа: 





On 3/11/21 12:30 PM, Ulrich Windl wrote:
> Hi!
>
> I wonder: Is it possible to register some callback to sbd that is called whenever a fencing operation is to be executed?
> I would like to run some command on the node that is going to be fenced.
Don't know of anything that exists you could use for that purpose.
Because of the base-principle it is anyway never gonna be reliable
that the command is executed. When the watchdog is taking
down the node you can't execute anything before of course.
And we couldn't wait for your callback to return of course as
we don't have a reliable channel back to the fencing party
and thus have to execute with a strict timeout.

What you can of course always do is put some pseudo-fence-agent
on a topology level with the poison-pill agent that tries to contact
the to be fenced party first to execute your command.

What I could imagine is to trigger execution of a customizable
command(s) in parallel with the sequence of reboot / sysrq
or as a replacement of that. We would still have the watchdog
to take care of a strict timeout.
I suppose idea is trying to do something graceful before being
taken down by the watchdog.
Or were you thinking along those lines:
https://bugzilla.redhat.com/show_bug.cgi?id=1869728


Regards,
Klaus
>
> Regards,
> Ulrich
>
>
>
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