[ClusterLabs] Parallel execution of resources in resource group

[Kab Naj]

Hello,

thank you very much for possible alternatives.
I still prefer if group unordered resources were possible, but probably
there was no demand for it.

I understand that in all three provided options I wouldn't use resource
groups at all.

In option 2 - "all with A" trick, I would use A as element to move the
whole "group".
In option 3 - I would use a tag as reference the whole "group", right?

In pcs implementation, can I move a "group" by naming a tag of ordering or
colocation resource sets ?

I will need to test the behavior of cluster while moving, clearing,
cleanup,..
All my co-workers are used to "resource/service groups" as reference
points, so I will need to change the procedures and the way of thinking.

Regards

Jan


On Thu, May 7, 2020 at 7:04 PM Ken Gaillot <kgaillot at redhat.com> wrote:

> Hi,
>
> You have a few alternatives to groups.
>
> 1 - You can configure independent colocation constraints for each
> resource. E.g. "B with A", "C with B", etc. This has the advantage that
> if you just want all the resources on the same node, you could colocate
> all later resources with the first one ("B with A", "C with A", etc.),
> so that there's no dependency between later resources (only the first
> resource has to be active for any of the others to be active, taking
> into account any ordering constraints).
>
> 2 - You can use resource sets in colocation constraints. You can do the
> "all with A" trick with this method using two resource sets, one with
> just A and the other non-sequential with all the rest. See:
>
>
> https://clusterlabs.org/pacemaker/doc/en-US/Pacemaker/2.0/html-single/Pacemaker_Explained/index.html#s-resource-sets-colocation
>
> 3 - You can use tags, and use a tag in a colocation constraint resource
> set. The main advantage of this approach would be if you want to use
> the logical group in more than one place. See:
>
>
> https://clusterlabs.org/pacemaker/doc/en-US/Pacemaker/2.0/html-single/Pacemaker_Explained/index.html#_tagging_configuration_elements
>
>
> On Thu, 2020-05-07 at 18:06 +0200, Kab Naj wrote:
> > Hello,
> >
> > I was trying to set parallel execution of resources in resource
> > group, but I was not successful.
> > The goal was to have resources within one resource group in one
> > location but order of resources would rely on Ordering constraints,
> > thus possibly resources could run in parallel if constraints allowed
> > it.
> >
> > By default it is not the case and resources run one by one in their
> > order of resource group.
> > I found the option that is designed to be used in resource clones -
> > "ordered"
> > ordered - Should the copies be started in series (instead of in
> > parallel). Allowed values: false, true.
> >
> > I tried to use this option in my resource group by setting
> > "ordered=false"
> > Resources could be started in parallel then, but I encountered
> > strange and unpredictable behavior when some resource start was not
> > successful.
> >
> > I understand that "ordered=false" is documented to be used only in
> > resource clones, not in resource groups.
> >
> > Do we have other option that resources within resource group would
> > start in parallel and rely on Ordering constraints, not their
> > resource group order?
> > We have many logical resource groups, so we don't want to have
> > resources without being added to any resource group.
> >
> > Regards
> >
> > Jan
> --
> Ken Gaillot <kgaillot at redhat.com>
>
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