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

Sylvain Bauza sylvain.bauza at gmail.com
Wed Mar 26 20:34:01 UTC 2014

I can't agree more on this. Although the name sounds identical to AWS, Nova
AZs are *not* for segregating compute nodes, but rather exposing to users a
certain sort of grouping.
Please see this pointer for more info if needed :

Regarding the bug mentioned by Vish [1], I'm the owner of it. I took it a
while ago, but things and priorities changed so I can take a look over it
this week and hope to deliver a patch by next week.


[1] https://bugs.launchpad.net/nova/+bug/1277230

2014-03-26 19:00 GMT+01:00 Chris Friesen <chris.friesen at windriver.com>:

> On 03/26/2014 11:17 AM, Khanh-Toan Tran wrote:
>  I don't know why you need a
>> compute node that belongs to 2 different availability-zones. Maybe
>> I'm wrong but for me it's logical that availability-zones do not
>> share the same compute nodes. The "availability-zones" have the role
>> of partition your compute nodes into "zones" that are physically
>> separated (in large term it would require separation of physical
>> servers, networking equipments, power sources, etc). So that when
>> user deploys 2 VMs in 2 different zones, he knows that these VMs do
>> not fall into a same host and if some zone falls, the others continue
>> working, thus the client will not lose all of his VMs.
> See Vish's email.
> Even under the original meaning of availability zones you could
> realistically have multiple orthogonal availability zones based on "room",
> or "rack", or "network", or "dev" vs "production", or even "has_ssds" and a
> compute node could reasonably be part of several different zones because
> they're logically in different namespaces.
> Then an end-user could boot an instance, specifying "networkA", "dev", and
> "has_ssds" and only hosts that are part of all three zones would match.
> Even if they're not used for orthogonal purposes, multiple availability
> zones might make sense.  Currently availability zones are the only way an
> end-user has to specify anything about the compute host he wants to run on.
>  So it's not entirely surprising that people might want to overload them
> for purposes other than physical partitioning of machines.
> Chris
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