[openstack-dev] [nova][scheduler] Availability Zones and Host aggregates..

Day, Phil philip.day at hp.com
Thu Mar 27 17:48:27 UTC 2014

Sorry if I'm coming late to this thread, but why would you define AZs to cover "othognal zones" ?

AZs are a very specific form of aggregate - they provide a particular isolation schematic between the hosts (i.e. physical hosts are never in more than one AZ) - hence the "availability" in the name.

AZs are built on aggregates, and yes aggregates can overlap and aggreagtes are used for scheduling.

So if you want to schedule on features as well as (or instead of) physical isolation, then you can already:

- Create an aggregate that contains "hosts with fast CPUs"
- Create another aggregate that includes "hosts with SSDs"
- Write (or configure in some cases) schedule filters that look at something in the request (such as schedule hint, an image property, or a flavor extra_spec) so that the scheduler can filter on those aggregates

nova boot --availability-zone az1 --scheduler-hint want-fast-cpu --scheduler-hint want-ssd  ...

nova boot --availability-zone az1 --flavor 1000    
(where flavor 1000 has extra spec that says it needs fast cpu and ssd)

But there is no need that I can see to make AZs overlapping just to so the same thing - that would break what everyone (including folks used to working with AWS) expects from an AZ

> -----Original Message-----
> From: Chris Friesen [mailto:chris.friesen at windriver.com]
> Sent: 27 March 2014 13:18
> To: openstack-dev at lists.openstack.org
> Subject: Re: [openstack-dev] [nova][scheduler] Availability Zones and Host
> aggregates..
> On 03/27/2014 05:03 AM, Khanh-Toan Tran wrote:
> > Well, perhaps I didn't make it clearly enough. What I intended to say
> > is that user should be able to select a set of AZs in his request,
> > something like :
> >
> >      nova  boot   --flavor 2  --image ubuntu   --availability-zone
> > Z1  --availability-zone AZ2  vm1
> I think it would make more sense to make the availability-zone argument
> take a comma-separated list of zones.
> nova boot --flavor 2 --image ubuntu --availability-zone AZ1,AZ2 vm1
> Just to clarify, in a case like this we're talking about using the intersection of
> the two zones, right?  That's the only way that makes sense when using
> orthogonal zones like "hosts with fast CPUs" and "hosts with SSDs".
> Chris
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