[ClusterLabs] [EXT] Clarification on resource groups

[Windl, Ulrich]

Hi!

Assuming you know what "location" refers to. What you are doing makes very little sense IMHO:
When working on a service that needs some IP, it makes little sense to put the service in maintenance mode, but not the IP:
Imagine something bad happens to the network and the cluster wants to move the IP while you are working on the service. Would you want that to happen? Also (as I see it), to move the group, the cluster would stop the service first, but when it's in maintenance mode, it can't. So it can't move the group (and thus the IP neither).
Pertsonally I put the cluster in maintenance mode as a whole, preferably for a rather short time. Unless services fail very frequently, this seems to be a safe mode of operation to me.

Kind regards,
Ulrich Windl

> -----Original Message-----
> From: Users <users-bounces at clusterlabs.org> On Behalf Of Eugen Block
> Sent: Monday, January 13, 2025 1:17 PM
> To: users at clusterlabs.org
> Subject: [EXT] [ClusterLabs] Clarification on resource groups
> 
> Hi,
> 
> I'm hoping to get some clarification on my understanding of resource
> groups [0]. It states:
> 
> > One of the most common elements of a cluster is a set of resources
> > that need to be located together, start sequentially, and stop in
> > the reverse order.
> 
> Especially the "located together" attribute confuses me.
> 
> I'll try to provide some context:
> I have a couple of systemd services as clones and some multi-state
> resources such as galera and rabbitmq, running on two pacemaker nodes.
> In case of an upgrade or any kind of maintenance, I want to use the
> maintenance mode for some resources, but not all of them. For example,
> I want the virtual IP, galera and rabbitmq to be still managed while
> the rest is in maintenance mode. So currently, I would run a for loop
> on the systemd services only, putting them into maintenance. This way,
> if the network stack is updated or something, the virtual IP would be
> moved to the other node. IIUC, this is not covered by the resource
> groups, is it?
> 
> Or should I have used it when building the cluster from scratch,
> creating groups containing my systemd services as primitives? And then
> clone a group?
> 
> Is there another way of achieving that? I'd appreciate any comments!
> 
> Thanks!
> Eugen
> 
> [0]
> https://clusterlabs.org/projects/pacemaker/doc/2.1/Pacemaker_Explained/
> singlehtml/index.html#group-resources
> 
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