[ClusterLabs] [EXT] Re: Clarification on resource groups

[Windl, Ulrich]

Hi!

Maybe you should show the resources and their dependencies. If the VIP is in a group, what else is in that group?
In my first reading I thought you want to manage one resource in a group, but still want the group to move. Is that right?

Kind regards,
Ulrich Windl

> -----Original Message-----
> From: Users <users-bounces at clusterlabs.org> On Behalf Of Eugen Block
> Sent: Monday, January 27, 2025 3:41 PM
> To: Cluster Labs - All topics related to open-source clustering welcomed
> <users at clusterlabs.org>
> Subject: [EXT] Re: [ClusterLabs] Clarification on resource groups
> 
> Thanks for your response.
> 
> Maybe I didn't explain myself well enough, I can go into more detail
> if necessary. I wanted to focus on resource groups first. But let me
> give an example from a recent upgrade that didn't go as smooth as
> planned.
> 
> We have a virtual IP colocated with haproxy, which redirects
> (OpenStack) API calls to the backend servers. Since there are multiple
> instances of those API services running, the services are still
> responsive and functioning properly.
> So I put one node in maintenance mode to be able to stop all the
> systemd units wrt OpenStack, but not Galera and RabbitMQ. This node
> didn't have the VIP at the time. When I was done with the first node,
> everything was still good. But putting the node with the VIP into
> maintenance mode was a mistake:
> 
> During the system update there were also updates for network related
> packages (I hadn't noticed that on the first node), leading to a
> restart of the network service, causing the VIP to vanish. But since
> pacemaker couldn't move the resource, we had an API outage for
> OpenStack. To avoid that in the future, I will only put some of the
> resources into maintenance mode, not all of them. That way pacemaker
> will be able to move the VIP and HAProxy to the already upgraded node,
> so there will only be a tiny disruption, but most clients won't
> notice. I successfully tested that behavior on a test cloud, hence I'm
> confident that this is the right approach in my case.
> 
> If I put the entire cluster into maintenance mode, the VIP wouldn't be
> moved away when the network gets interrupted, that would cause a
> client disruption.
> 
> Thanks!
> Eugen
> 
> 
> Zitat von "Windl, Ulrich" <u.windl at ukr.de>:
> 
> > 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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> 
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