[ClusterLabs] Antw: Re: spread out resources

[Ulrich Windl]

Hi!

Actually form my SLES11 SP[1-4] experience, the cluster always distributes
resources across all available nodes, and only if don't want that, I'll have to
add constraints. I wonder why that does not seem to work for you.

Regards,
Ulrich

>>> Ferenc Wágner <wferi at niif.hu> schrieb am 02.04.2016 um 10:28 in Nachricht
<87egao9zyc.fsf at lant.ki.iif.hu>:
> Ken Gaillot <kgaillot at redhat.com> writes:
> 
>> On 03/30/2016 08:37 PM, Ferenc Wágner wrote:
>> 
>>> I've got a couple of resources (A, B, C, D, ... more than cluster nodes)
>>> that I want to spread out to different nodes as much as possible.  They
>>> are all the same, there's no distinguished one amongst them.  I tried
>>> 
>>> <rsc_colocation id="cl-test-spread" score="-50">
>>>   <resource_set id="cl-test-spread-set" sequential="false">
>>>     <resource_ref id="A"/>
>>>     <resource_ref id="B"/>
>>>     <resource_ref id="C"/>
>>>     <resource_ref id="D"/>
>>>   </resource_set>
>>>   <resource_set id-ref="cl-test-spread-set"/>
>>> </rsc_colocation>
>>> 
>>> But crm_simulate did not finish with the above in the CIB.
>>> What's a good way to get this working?
>>
>> Per the docs, "A colocated set with sequential=false makes sense only if
>> there is another set in the constraint. Otherwise, the constraint has no
>> effect." Using sequential=false would allow another set to depend on all
>> these resources, without them depending on each other.
> 
> That was the very idea behind the above colocation constraint: it
> contains the same group twice.  Yeah, it's somewhat contrived, but I had
> no other idea with any chance of success.  And this one failed as well.
> 
>> I haven't actually tried resource sets with negative scores, so I'm not
>> sure what happens there. With sequential=true, I'd guess that each
>> resource would avoid the resource listed before it, but not necessarily
>> any of the others.
> 
> Probably, but that isn't what I'm after.
> 
>> By default, pacemaker does spread things out as evenly as possible, so I
>> don't think anything special is needed.
> 
> Yes, but only on the scale of all resources.  And I've also got a
> hundred independent ones, which wash out this global spreading effect if
> you consider only a select handful.
> 
>> If you want more control over the assignment, you can look into
>> placement strategies:
> 
> We use balanced placement to account for the different memory
> requirements of the various resources globally.  It would be possible to
> introduce a new, artifical utilization "dimension" for each resource
> group we want to spread independently, but this doesn't sound very
> compelling.  For sets of two resources, a simple negative colocation
> constraint works very well; it'd be a pity if it wasn't possible to
> extend this concept to larger sets.
> -- 
> Thanks,
> Feri
> 
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