Open Stack

On Apr 25, 2014, at 2:15 PM, Jay Pipes <jaypipes at gmail.com> wrote:

> Hi Stackers,
> 
> When recently digging in to the new server group v3 API extension
> introduced in Icehouse, I was struck with a bit of cognitive dissonance
> that I can't seem to shake. While I understand and support the idea
> behind the feature (affinity and anti-affinity scheduling hints), I
> can't help but feel the implementation is half-baked and results in a
> very awkward user experience.

I agree with all you said about this.

> Proposal
> --------
> 
> I propose to scrap the server groups API entirely and replace it with a
> simpler way to accomplish the same basic thing.
> 
> Create two new options to nova boot:
> 
> --near-tag <TAG>
> and
> --not-near-tag <TAG>
> 
> The first would tell the scheduler to place the new VM near other VMs
> having a particular "tag". The latter would tell the scheduler to place
> the new VM *not* near other VMs with a particular tag.
> 
> What is a "tag"? Well, currently, since the Compute API doesn't have a
> concept of a single string tag, the tag could be a key=value pair that
> would be matched against the server extra properties.

You can actually already achieve this behavior… although with a little more work. There’s the Affinty filter which allows you to specify a same_host/different_host scheduler hint where you explicitly specify the instance uuids you want…  (the extra work is having to know the instance uuids).

But yeah, I think this makes more sense to me.

- Chris