[Pacemaker] Dependency Trees

[Jake Smith]

----- Original Message -----
> From: "Donald Stahl" <don at blacksun.org>
> To: "The Pacemaker cluster resource manager" <pacemaker at oss.clusterlabs.org>
> Sent: Thursday, February 21, 2013 9:40:06 AM
> Subject: Re: [Pacemaker] Dependency Trees
> 
> > No.
> >
> > [quote]
> > If you say "colocate A with B" and there is nowhere B is allowed to
> > run, then A wont be allowed to run either.
> > But once the cluster has figured out where they go, it doesn't stop
> > them being started in parallel.
> > [/quote]
> >
> > in this case, A = OraListener1 and B = OraBin1
> >
> > You only get the "Start A then start B" part by adding the ordering
> > constraint.
> 
> I'm not sure I understand where the "sequential" option comes into
> play with a colocation set then.
> 
> Or to put it another way- I'm not sure what practical difference
> there
> is in these examples:
> 
> http://clusterlabs.org/wiki/FAQ#Collocation_Sets

I think you may have missed a key piece - Sets.  Requires more than 2 and assumes at least one will be sequential.

Here might explain better - have a look at the "Unversioned Docs" at 'General Concepts' - ordering explained and colocation explained.  Well into each of the documents they talk about sequential/non-sequential:

http://clusterlabs.org/doc/


> 
> colocation myset inf: app1 app2
> colocation myset inf: ( app1 app2 )

Basics are something like this:
colocation myset inf: ( app1 app2 ) app3

app1 and app2 don't care about each other but they both must colocate with app3.  App2's locale/status doesn't effect app1 but app3 effects both whereas

colocation myset inf: app1 app2 app3

app2 can only run once app3 is placed and app1 can only run once app3 and app2 are placed.

> 
> The first seems to say that app1 is dependent on app2 being able to
> run somewhere.
> 
> Does the second one simply say that they must not be split up, but if
> only one can run, that's fine?
> 
> -Don
> 
> _______________________________________________
> Pacemaker mailing list: Pacemaker at oss.clusterlabs.org
> http://oss.clusterlabs.org/mailman/listinfo/pacemaker
> 
> Project Home: http://www.clusterlabs.org
> Getting started:
> http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
> Bugs: http://bugs.clusterlabs.org
> 
>