[openstack-dev] [nova] do not account compute resource of instances in state SHELVED_OFFLOADED

Andrew Laski andrew at lascii.com
Wed Jan 27 09:38:35 UTC 2016

On Tue, Jan 26, 2016, at 07:46 AM, Christian Berendt wrote:
> After offloading a shelved instance the freed compute resources are 
> still accounted.
> I think it makes sense to make this behavior configurable. We often have 
> the request to not account the freed compute resources after an 
> instances was offloaded to be able to spawn new instances or to 
> unshelved offloaded instances even the assigned compute resource quota 
> was archieved.
> Because the instance are shelved and offloaded they do not occupy 
> compute resource and it is often safe to allow the freed compute 
> resources for other inststances. Of coure it has to be checked if there 
> are enough free compute resource when trying to unshelve an offloaded 
> instance.
> What do you thin about this use case? If it make sense to you I want to 
> propose to write a spec for this feature.

I would really prefer if we could standardize on either counting the
resources against quota or not.  However this seems unlikely since
deployers offer shelving functionality for different reasons.  I think
it's worth proposing the spec and getting operator feedback on it.

My two primary concerns with freeing up quota resources for offloaded
instances are:

1. This allows for a poor experience where a user would not be able to
turn on and use an instance that they already have due to overquota. 
This is a change from the current behavior where they just can't create
resources, now something they have is unusable.

2. I anticipate a further ask for a separate quota for the number of
offloaded resources being used to prevent just continually spinning up
and shelving instances with no limit.  Because while disk/ram/cpu
resources are not being consumed by an offloaded instance network and
volume resources remain consumed and storage is required is Glance for
the offloaded disk.  And adding this additional quota adds more
complexity to shelving which is already overly complex and not well

> Christian.
> -- 
> Christian Berendt
> Cloud Solution Architect
> Mail: berendt at b1-systems.de
> B1 Systems GmbH
> Osterfeldstraße 7 / 85088 Vohburg / http://www.b1-systems.de
> GF: Ralph Dehner / Unternehmenssitz: Vohburg / AG: Ingolstadt,HRB 3537
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