[ClusterLabs] trigger something at ?

[Jehan-Guillaume de Rorthais]

On Wed, 31 Jan 2024 16:37:21 +0100
lejeczek via Users <users at clusterlabs.org> wrote:

> 
> 
> On 31/01/2024 16:06, Jehan-Guillaume de Rorthais wrote:
> > On Wed, 31 Jan 2024 16:02:12 +0100
> > lejeczek via Users <users at clusterlabs.org> wrote:
> >
> >>
> >> On 29/01/2024 17:22, Ken Gaillot wrote:
> >>> On Fri, 2024-01-26 at 13:55 +0100, lejeczek via Users wrote:
> >>>> Hi guys.
> >>>>
> >>>> Is it possible to trigger some... action - I'm thinking specifically
> >>>> at shutdown/start.
> >>>> If not within the cluster then - if you do that - perhaps outside.
> >>>> I would like to create/remove constraints, when cluster starts &
> >>>> stops, respectively.
> >>>>
> >>>> many thanks, L.
> >>>>
> >>> You could use node status alerts for that, but it's risky for alert
> >>> agents to change the configuration (since that may result in more
> >>> alerts and potentially some sort of infinite loop).
> >>>
> >>> Pacemaker has no concept of a full cluster start/stop, only node
> >>> start/stop. You could approximate that by checking whether the node
> >>> receiving the alert is the only active node.
> >>>
> >>> Another possibility would be to write a resource agent that does what
> >>> you want and order everything else after it. However it's even more
> >>> risky for a resource agent to modify the configuration.
> >>>
> >>> Finally you could write a systemd unit to do what you want and order it
> >>> after pacemaker.
> >>>
> >>> What's wrong with leaving the constraints permanently configured?
> >> yes, that would be for a node start/stop
> >> I struggle with using constraints to move pgsql (PAF) master
> >> onto a given node - seems that co/locating paf's master
> >> results in troubles (replication brakes) at/after node
> >> shutdown/reboot (not always, but way too often)
> > What? What's wrong with colocating PAF's masters exactly? How does it brake
> > any replication? What's these constraints you are dealing with?
> >
> > Could you share your configuration?
> Constraints beyond/above of what is required by PAF agent 
> itself, say...
> you have multiple pgSQL cluster with PAF - thus multiple 
> (separate, for each pgSQL cluster) masters and you want to 
> spread/balance those across HA cluster
> (or in other words - avoid having more that 1 pgsql master 
> per HA node)

ok

> These below, I've tried, those move the master onto chosen 
> node but.. then the issues I mentioned.

You just mentioned it breaks the replication, but there so little information
about your architecture and configuration, it's impossible to imagine how this
could break the replication.

Could you add details about the issues ?

> -> $ pcs constraint location PGSQL-PAF-5438-clone prefers 
> ubusrv1=1002
> or
> -> $ pcs constraint colocation set PGSQL-PAF-5435-clone 
> PGSQL-PAF-5434-clone PGSQL-PAF-5433-clone role=Master 
> require-all=false setoptions score=-1000

I suppose "collocation" constraint is the way to go, not the "location" one.