[ClusterLabs] Q: constrain or delay "probes"?

[Ken Gaillot]

On Fri, 2021-03-05 at 11:39 +0100, Ulrich Windl wrote:
> Hi!
> 
> I'm unsure what actually causes a problem I see (a resource was
> "detected running" when it actually was not), but I'm sure some probe
> started on cluster node start cannot provide a useful result until
> some other resource has been started. AFAIK there is no way to make a
> probe obey odering or colocation constraints, so the only work-around 
> seems to be a delay. However I'm unsure whether probes can actually
> be delayed.
> 
> Ideas?

Ordered probes are a thorny problem that we've never been able to come
up with a general solution for. We do order certain probes where we
have enough information to know it's safe. The problem is that it is
very easy to introduce ordering loops.

I don't remember if there any workarounds.

> Despite of that I wonder whether some probe/monitor returncode like
> OCF_NOT_READY would make sense if the operation detects that it
> cannot return a current status (so both "running" and "stopped" would
> be as inadequate as "starting" and "stopping" would be (despite of
> the fact that the latter two do not exist)).
>
> Regards,
> Ulrich
-- 
Ken Gaillot <kgaillot at redhat.com>