[Pacemaker] Simple way to prefer resource groups not start on the same node

[Dejan Muhamedagic]

Hi,

On Wed, Aug 25, 2010 at 10:30:39AM -0500, Matthew Schlegel wrote:
> 
> > -----Original Message-----
> > From: Dejan Muhamedagic [mailto:dejanmm at fastmail.fm]
> > 
> > Hi,
> > 
> > On Tue, Aug 24, 2010 at 08:54:58AM -0500, Matthew Schlegel wrote:
> > > Howdy,
> > 
> > Pacemaker will try to balance the number of resources running on
> > each node. Not perfect, but there's a good chance that no single
> > node will run all the resources as you suggest.
> > 
> > I think that doing location preferences is the right way to deal
> > with this:
> > 
> > location l-mysql1 mysql1 100: node1
> > etc
> > 
> > If node1 fails, mysql1 would move elsewhere. If the mysql1 fails,
> > then you can use migration-threshold to control how many times to
> > try to restart it. Use resource-stickiness to control when
> > resources fail back.
> > 
> > Finally, how often do you expect your resources/nodes to fail?
> > 
> > Thanks,
> > 
> > Dejan
> > 
> 
> Howdy,
> 
> In normal operations, I don't expect failures to occur very
> often.   One of the potential failure points would be power
> related, which would potentially take down half the nodes.
> 
> I have seen already that without any constraints applied, I end
> up with one node idle and two of the mysql resource groups
> running on one node.  Based on that, I'm hesitant to just let
> pacemaker completely do its own.

That's strange. Though there are no guarantees, pengine should
distribute resources as best as it can. Perhaps it was due to
resources failing earlier on the node which wasn't assigned any.
You can always check the scores if you have the PE input file.

> For now, I'll hook them up with location constraints to cover
> normal operation, and keep digging for a good way to handle
> balancing the resource groups in failure conditions.

OK. Whatever you do, try to keep the configuration manageable and
as simple as possible.

Thanks,

Dejan

> Thank you,
> 
> Matthew Schlegel
> System Analyst
> 
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