[ClusterLabs] Interleaving clones with different number of instances per node

[Ken Gaillot]

On Mon, 2024-10-14 at 18:49 +0200, Jochen wrote:
> Hi, I have two cloned resources in my cluster that have the following
> properties:
> 
> * There are a maximum of two instances of R1 in the cluster, with a
> maximum of two per node
> * When any instance of R1 is started on a node, exactly one instance
> of R2 should run on that node
> 
> When I configure this, and verify the configuration with "crm_verify
> -LV", I get the following error:
> 
> clone_rsc_colocation_rh) 	error: Cannot interleave R2-clone and
> R1-clone because they do not support the same number of instances per
> node
> 
> How can I make this work? Any help would be greatly appreciated.

Hi,

I believe the number of instances has to be the same because each
instance pair on a single node is interleaved.

There's no direct way to configure what you want, but it might be
possible with a custom OCF agent for R1 and attribute-based rules.

On start, the R1 agent could set a custom node attribute to some value.
On stop, it could check whether any other instances are active
(assuming that's possible), and if not, clear the attribute. Then, R2
could have a location rule enabling it only on nodes where the
attribute has the desired value.

R2 wouldn't stop until *after* the last instance of R1 stops, which
could be a problem depending on the particulars of the service. There
might also be a race condition if two instances are stopping at the
same time, so it might be worthwhile to set ordered=true on the clone.

> 
> 
> Current configuration is as follows:
> 
> <resources>
>   <clone id="R1-clone">
>     <meta_attributes id="R1-clone-meta_attributes">
>       <nvpair name="interleave" value="true" id="R1-clone-
> meta_attributes-interleave"/>
>       <nvpair name="resource-stickiness" value="0" id="R1-clone-
> meta_attributes-resource-stickiness"/>
>       <nvpair name="clone-max" value="2" id="R1-clone-
> meta_attributes-clone-max"/>
>       <nvpair name="clone-node-max" value="2" id="R1-clone-
> meta_attributes-clone-node-max"/>
>       <nvpair name="globally-unique" value="true" id="R1-clone-
> meta_attributes-globally-unique"/>
>       <nvpair name="failure-timeout" value="300" id="R1-clone-
> meta_attributes-failure-timeout"/>
>       <nvpair name="migration-threshold" value="0" id="R1-clone-
> meta_attributes-migration-threshold"/>
>       <nvpair id="R1-clone-meta_attributes-target-role" name="target-
> role" value="Stopped"/>
>     </meta_attributes>
>   </clone>
>   <clone id="R2-clone">
>     <meta_attributes id="R2-clone-meta_attributes">
>       <nvpair name="interleave" value="true" id="R2-clone-
> meta_attributes-interleave"/>
>       <nvpair name="resource-stickiness" value="0" id="R2-clone-
> meta_attributes-resource-stickiness"/>
>       <nvpair name="failure-timeout" value="300" id="R2-clone-
> meta_attributes-failure-timeout"/>
>       <nvpair name="migration-threshold" value="0" id="R2-clone-
> meta_attributes-migration-threshold"/>
>       <nvpair id="R2-clone-meta_attributes-target-role" name="target-
> role" value="Stopped"/>
>     </meta_attributes>
>   </clone>
> </resources>
> 
> <constraints>
>   <rsc_order id="R1-order" kind="Mandatory" first="R1-clone"
> then="R2-clone"/>
>   <rsc_colocation id="R2-clone-colocation" score="INFINITY" rsc="R2-
> clone" with-rsc="R1-clone"/>
> </constraints>
> 
> 
-- 
Ken Gaillot <kgaillot at redhat.com>