[ClusterLabs] trigger something at ?

lejeczek peljasz at yahoo.co.uk
Wed Jan 31 10:37:21 EST 2024

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 
-> $ pcs constraint colocation set PGSQL-PAF-5435-clone 
PGSQL-PAF-5434-clone PGSQL-PAF-5433-clone role=Master 
require-all=false setoptions score=-1000

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