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

Chris Friesen chris.friesen at windriver.com
Wed Mar 26 18:00:01 UTC 2014

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.


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