[ClusterLabs] trigger something at ?

[Ken Gaillot]

On Thu, 2024-02-01 at 14:31 +0100, lejeczek via Users wrote:
> 
> On 31/01/2024 18:11, Ken Gaillot wrote:
> > On Wed, 2024-01-31 at 16:37 +0100, lejeczek via Users 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)
> > > These below, I've tried, those move the master onto chosen
> > > node but.. then the issues I mentioned.
> > > 
> > > -> $ 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
> > > 
> > Anti-colocation sets tend to be tricky currently -- if the first
> > resource can't be assigned to a node, none of them can. We have an
> > idea
> > for a better implementation:
> > 
> >   https://projects.clusterlabs.org/T383
> > 
> > In the meantime, a possible workaround is to use placement-
> > strategy=balanced and define utilization for the clones only. The
> > promoted roles will each get a slight additional utilization, and
> > the
> > cluster should spread them out across nodes whenever possible. I
> > don't
> > know if that will avoid the replication issues but it may be worth
> > a
> > try.
> using _balanced_ causes a small mayhem to PAF/pgsql:
> 
> -> $ pcs property
> Cluster Properties:
>   REDIS-6380_REPL_INFO: ubusrv3
>   REDIS-6381_REPL_INFO: ubusrv2
>   REDIS-6382_REPL_INFO: ubusrv2
>   REDIS-6385_REPL_INFO: ubusrv1
>   REDIS_REPL_INFO: ubusrv1
>   cluster-infrastructure: corosync
>   cluster-name: ubusrv
>   dc-version: 2.1.2-ada5c3b36e2
>   have-watchdog: false
>   last-lrm-refresh: 1706711588
>   placement-strategy: default
>   stonith-enabled: false
> 
> -> $ pcs resource utilization PGSQL-PAF-5438 cpu="20"
> 
> -> $ pcs property set placement-strategy=balanced # when 
> resource stops:
> I change it back:
> -> $ pcs property set placement-strategy=default
> and pgSQL/paf works again
> 
> I've not used _utilization_ nor _placement-strategy_ before, 
> thus chance that I'm missing something is solid.
> 

See:

https://clusterlabs.org/pacemaker/doc/2.1/Pacemaker_Explained/html/utilization.html

You have to define the node capacities as well as the resource
utilization. I'd define the capacities high enough to run all the
resources (assuming you want that capability if all other nodes are in
standby or whatever). 
-- 
Ken Gaillot <kgaillot at redhat.com>