[Pacemaker] Order Constraint for: stop rscA only when rscB is running ?

[Andreas Kurz]

On Monday 06 October 2008 15:36:31 Andrew Beekhof wrote:
> On Thu, Oct 2, 2008 at 10:23, Andreas Kurz <andreas.kurz at linbit.com> wrote:
> > Hi,
> >
> > I have a Heartbeat 2.1.3 two-node cluster and I wonder if there is a way
> > to create constraints that work like that:
> >
> > * Two resources (rscA and rscB) of class "heartbeat" that should run
> > together on one node .... simple advisory colocation constraint
> >
> > <rsc_colocation id="rscA-colocated-with-rscB"
> >        from="rscA" to="rscB"
> >        score="1" symmetrical="true"/>
> >
> > * When doing maintenance on one node I put the node into standby mode and
> > want rscA only stop and migrate away if rscB is already up and running on
> > the other node and vice versa because  there must always run at least one
> > of these resources in the cluster.
> >
> > I added two order_constraints and tested it with ptest on an adapted live
> > cib but they seem to produce a loop:
>
> This is logical if you draw it out (and remember that Stop X always
> precedes Start X)

Yes, I expected a loop and I had a slide hope there is some 
cool "prevent-loops" logic available ;-)

>
> Any reason not to just use the following?
>
> <rsc_order id="always-start-A-after-B"
>        from="service_rscB" action="start"
>        type="before"
>        to="service_rscA" to_action="start"
>        symmetrical="true" score="0"/>

The reason is that first rscA then rscB ist stopped ... so they are both down 
before they are restarted in this order on the other node.

The idea is ... in case of a manual switchover of all services from nodeA to 
nodeB during regular failover tests, rscA should be stopped on nodeA _after_ 
rscB is already _started_ on nodeB. 

Regards,
Andreas

>
> > <rsc_order id="stop-rscA-only-after-rscB-start"
> >        from="service_rscA" action="stop"
> >        type="after"
> >        to="service_rscB" to_action="start"
> >        symmetrical="false" score="0"/>
> >
> > <rsc_order id="stop-rscB-only-after-rscA-start"
> >        from="service_rscB" action="stop"
> >        type="after"
> >        to="service_rscA" to_action="start"
> >        symmetrical="false" score="0"/>
> >
> > Is there a way to get the requested behavior or is a manual resource
> > after resource migration the only way to achieve this?
> >
> > Regards,
> > Andreas
...

-- 
: Andreas Kurz					 
: LINBIT | Your Way to High Availability
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