Open Stack

On 2016-03-03 12:50 PM, Silence Dogood wrote:
> We did some early affinity work and discovered some interesting problems
> with affinity and scheduling. =/  by default openstack used to ( may
> still ) deploy nodes across hosts evenly.  
> 
> Personally, I think this is a bad approach.  Most cloud providers stack
> across a couple racks at a time filling them then moving to the next. 
> This allows older equipment to age out instances more easily for removal
> / replacement.  
> 
> The problem then is, if you have super large capacity instances they can
> never be deployed once you've got enough tiny instances deployed across
> the environment.  So now you are fighting with the scheduler to ensure
> you have deployment targets for specific instance types ( not very
> elastic / ephemeral ).  goes back to the wave scheduling model being
> superior.  
> 
> Anyways we had the braindead idea of locking whole physical nodes out
> from the scheduler for a super ( full node ) instance type.  And I
> suppose you could do this with AZs or regions if you really needed to. 
> But, it's not a great approach.
> 
> I would say that you almost need a wave style scheduler to do this sort
> of affinity work.
> 

You can already do it with the RAMWeigher using the
ram_weight_multiplier config:

  Multiplier used for weighing ram.  Negative
  numbers mean to stack vs spread.

Default is 1.0 which means spread.

-- 
Mathieu