[ClusterLabs] Coming in Pacemaker 2.1.3: multiple-active=stop_unexpected

[Andrei Borzenkov]

On 08.04.2022 20:16, Ken Gaillot wrote:
> Hi all,
> 
> I'm hoping to have the first release candidate for Pacemaker 2.1.3
> available in a couple of weeks.
> 
> One of the new features will be a new possible value for the "multiple-
> active" resource meta-attribute, which specifies how the cluster should
> react if multiple instances of a resource are detected to be active
> when only one should be.
> 
> The default behavior, "restart", stops all the instances and then
> starts one instance where it should be. This is the safest approach
> since some services become disrupted when multiple copies are started.
> 
> However if the user is confident that only the extra copies need to be
> stopped, they can now set multiple-active to "stop_unexpected". The
> instance that is active where it is supposed to be will not be stopped,
> but all other instances will be.
> 
> If any resources are ordered after the multiply active resource, those
> other resources will still need to be fully restarted. This is because
> any ordering constraint "start A then start B" implies "stop B then
> stop A", so we can't stop the wrongly active instances of A until B is
> stopped.

But in the case of multiple-active=stop_unexpected "the correct" A does
remain active. If any dependent resource needs to be restarted anyway, I
miss the intended use case. What is the difference with default option
(except it may be faster)?