[Openstack] unexpected distribution of compute instances in queens

Matt Riedemann mriedemos at gmail.com
Mon Nov 26 20:40:51 UTC 2018

On 11/26/2018 10:13 AM, Sean Mooney wrote:
> hi, the default behavior of nova used to be spread not pack and i belive it still is.
> the default behavior with placement however is closer to a packing behavior as
> allcoation candiates are retrunidn in an undefined but deterministic order.
> on a busy cloud this does not strictly pack instaces but on a quite cloud it effectivly does
> you can try and enable randomisation of the allocation candiates by setting this config option in
> the nova.conf of the shcduler to true.
> https://docs.openstack.org/nova/latest/configuration/config.html#placement.randomize_allocation_candidates
> on that note can you provide the nova.conf for the schduelr is used instead of the compute node nova.conf.
> if you have not overriden any of the nova defaults the ram and cpu weigher should spread instances withing
> the allocation candiates returned by placement.

Or simply the other hosts are being filtered out, either because they 
aren't reporting into placement or some other filter is removing them. 
You should be able to see which hosts are being filtered if you enable 
debug logging in the nova-scheduler process (via the "debug" 
configuration option).




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