[Pacemaker] Dependency Trees

[Andrew Beekhof]

On Fri, Feb 22, 2013 at 1:40 AM, Donald Stahl <don at blacksun.org> wrote:
>> 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
>
> colocation myset inf: app1 app2
> colocation myset inf: ( app1 app2 )

I'm pretty sure the latter doesn't do anything (bad choice of defaults
by the crmsh) because the set isn't colocated with anything.

You'd need something as well as the set for it to make sense,  eg.

   colocation myset inf: app0 ( app1 app2 )

> 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
>
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