[Pacemaker] Load Balancing, Node Scores and Stickiness

[Andrew Beekhof]

On Wed, Oct 21, 2009 at 2:06 PM, Colin <colin.hch at gmail.com> wrote:
> Hi All,
>
> it seems from the documentation that Pacemaker has some inherent
> tendency to to load-balancing, in the sense of, given equal choice,
> not starting all resources on a single node...
>
> Now, I would like to be able to choose freely on a scale between
> "always move everything to achieve good load balancing" and "don't
> gratuitously migrate resources", and would therefore like to
> understand the algorithms in Pacemaker better.
>
> Given a bunch of nodes and resources with a simple setup, i.e. no
> resource colocation constraints, no groups etc., I understand that a
> global score is calculated for each resource and each node, where
>
> score( resource, node ) = sum of all rsc_location constraints for that
> resource and node + if the resource is already running on this node,
> the stickiness (the stickiness of the resource or the global default
> stickiness)
>
> How does the assignment of nodes proceed? My guess is something like:
>
> for every resource in order of resource priority
>   choose node with highest score for that resource

     if multiple nodes exist with the same score, pick one with the
least allocated resources

>   ??? somehow modify scores to prevent all resources on one node
>
> Are the details documented anywhere [except for the source]?

Just the source so far