[ClusterLabs] Parallel execution of resources in resource group

[Ken Gaillot]

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>