[ClusterLabs] question about equal resource distribution

[Kristoffer Grönlund]

Ilia Sokolinski <ilia at clearskydata.com> writes:

> Thank you!
>
> What quantity does pacemaker tries to equalize - number of running resources per node or total stickiness per node?
>

I honestly don't know exactly what the criteria are. Without any
utilization definitions for nodes, I *think* it tries to balance the
number of resources per node. But if the resources and nodes have
cpu/memory utilization defined, the rules change. But I'm afraid I
haven't dug into exactly what the logic looks like.

> Suppose I have a bunch of web server groups each with IPaddr and apache resources, and a fewer number of database groups each with IPaddr, postgres and LVM resources.
>
> In that case, does it mean that 3 web server groups are weighted the same as 2 database groups in terms of distribution?

Good question, I think it looks purely at the primitive
resources. Groups are just shorthand for a series of ordering and
placement constraints.

Cheers,
Kristoffer

>
> Ilia
>
>
>
>> On Feb 17, 2017, at 2:58 AM, Kristoffer Grönlund <deceiver.g at gmail.com> wrote:
>> 
>> Ilia Sokolinski <ilia at clearskydata.com> writes:
>> 
>>> Suppose I have a N node cluster where N > 2 running m*N resources. Resources don’t have preferred nodes, but since resources take RAM and CPU it is important to distribute them equally among the nodes.
>>> Will pacemaker do the equal distribution, e.g. m resources per node?
>>> If a node fails, will pacemaker redistribute the resources equally too, e.g. m * N/(N-1) per node?
>>> 
>>> I don’t see any settings controlling this behavior in the documentation, but perhaps, pacemaker tries to be “fair” by default.
>>> 
>> 
>> Yes, pacemaker tries to allocate resources evenly by default, and will
>> move resources when nodes fail in order to maintain that.
>> 
>> There are several different mechanisms that influence this behaviour:
>> 
>> * Any placement constraints in general influence where resources are
>>  allocated.
>> 
>> * You can set resource-stickiness to a non-zero value which determines
>>  to which degree Pacemaker prefers to leave resources running where
>>  they are. The score is in relation to other placement scores, like
>>  constraint scores etc. This can be set for individual resources or
>>  globally. [1]
>> 
>> * If you have an asymmetrical cluster, resources have to be manually
>>  allocated to nodes via constraints, see [2]
>> 
>> [1]: http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#s-resource-options
>> [2]: http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#_asymmetrical_opt_in_clusters
>> 
>> Cheers,
>> Kristoffer
>> 
>>> Thanks 
>>> 
>>> Ilia Sokolinski
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>> 
>> -- 
>> // Kristoffer Grönlund
>> // kgronlund at suse.com
>
>
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-- 
// Kristoffer Grönlund
// kgronlund at suse.com