[Openstack] [nova] Nova-scheduler: when are filters applied?

Eugen Block eblock at nde.ag
Thu Aug 30 14:21:11 UTC 2018

Sorry. I was to quick with the send button...

Hi *,

I posted my question in [1] a week ago, but no answer yet.

When does Nova apply its filters (Ram, CPU, etc.)?
Of course at instance creation and (live-)migration of existing
instances. But what about existing instances that have been shutdown
and in the meantime more instances on the same hypervisor have been

When you start one of the pre-existing instances and even with RAM
overcommitment you can end up with an OOM-Killer resulting in
forceful shutdowns if you reach the limits. Is there something I've
been missing or maybe a bad configuration of my scheduler filters? Or
is it the admin's task to keep an eye on the load?

I'd appreciate any insights or pointers to something I've missed.



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