Need information

Erik McCormick emccormick at
Fri Apr 29 17:28:03 UTC 2022

On Fri, Apr 29, 2022, 10:17 AM Gk Gk <ygk.kmr at> wrote:

> Hi All,
> I need information about availability zones in nova. I tried googling but
> cant find enough information. My questions are ,
> 1. Why  is it that we have two concepts of aggregates and AZs ? Is one not
> enough ? Like exposing aggregates and creating flavors with extra specs to
> match ? Why do we need AZs also ?

AZ isn't for picking the right type of host. It's for picking hosts that
are distributed. Maybe you want a host with local disk. Great, you use
aggregates / flavor specs for that. But what if you want instances for a
myself cluster or setting to each be in different racks? Then you need AZs.

> 2. Why is it that one node should only be a part of one AZ but not two ?
> whereas in the case of aggregates, it can overlap ?

Overlapping failure domains would be pretty confusing and pointless.

> 3. Also why cant we expose only aggregates like AZs but block the compute
> member list to the users ? Doing this way will serve the purpose of AZ as
> well ? Why we dont want to expose aggregates as AZs ?

They're mutually exclusive concepts.

> Thanks
> Kumar
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