[ClusterLabs] Q: Resource balancing opration

[Klaus Wenninger]

On 04/20/2016 08:17 AM, Ulrich Windl wrote:
> Hi!
>
> I'm wondering: If you boot a node on a cluster, most resources will go to another node (if possible). Due to stickiness configured, those resources will stay there.
> So I'm wondering whether or how I could cause a rebalance of resources on the cluster. I must admit that I don't understand the details of stickiness related to other parameters. In my understanding stickiness should be related to a percentage of utilization dynamically, so that a resource running on a node that is "almost full" should dynamically lower its stickiness to allow resource migration.
The only aim of stickiness is to prevent resources from switching back
and forth.
But you are free to balance it with other score-based mechanisms by
tuning the score-values. Just
be careful not to create anything that constantly switches resources
between nodes when the
stickiness becomes to small in comparison.
>
> So if you are going to implement a manual resource rebalance operation, could you dynamically lower the stickiness for each resource (by some amount or some factor), wait if something happens, and then repeat the process until resources look balanced. "Looking balanced" should be no worse as if all resources are started when all cluster nodes are up.
Main issue I see is how the cluster should know if a node is just
rebooting and thus should maybe wait before starting to rebalance or if
it has failed and rebalancing would be appreciated.
You could either inform the cluster ahead of a scheduled reboot (e.g.
maintenance-mode would be a way to do that)
or the cluster would have to wait a certain time to take certain actions
to leave the node enough time to come back online.
For the latter I don't know if there are meanwhile pacemaker features
that can be used directly for such. (To configure
the corosync-timing accordingly would certainly be a bad idea ;-) ) I
remember to have implemented the detection of
the loss of a node inside a daemon which then - after a certain time -
would modify a pacemaker-attribute which in
turn was used as part of resource-location rules.
 
>
> Spontaneous pros and cons for "resource rebalancing"?
>
> Regards,
> Ulrich
>
>
>
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