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>> ​To be honest this is probably my fault, AZ's were pulled in as part of
>> the nova-volume migration to Cinder and just sort of died.  Quite
>> frankly I wasn't sure "what" to do with them but brought over the
>> concept and the zones that existing in Nova-Volume.  It's been an issue
>> since day 1 of Cinder, and as you note there are little hacks here and
>> there over the years to do different things.
>>
>> I think your question about whether they should be there at all or not
>> is a good one.  We have had some interest from folks lately that want to
>> couple Nova and Cinder AZ's (I'm really not sure of any details or
>> use-cases here).
>>
>> My opinion would be until somebody proposes a clear use case and need
>> that actually works that we consider deprecating it.
>>
>> While we're on the subject (kinda) I've never been a very fond of having
>> Nova create the volume during boot process either; there's a number of
>> things that go wrong here (timeouts almost guaranteed for a "real"
>> image) and some things that are missing last I looked like type
>> selection etc.
>>
>> We do have a proposal to talk about this at the Summit, so maybe we'll
>> have a descent primer before we get there :)
>>
>> Thanks,
>>
>> John
>>
>>
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>
> Heh, so when I just asked in the cinder channel if we can just
> deprecate nova boot from volume with source=(image|snapshot|blank)
> (which automatically creates the volume and polls for it to be
> available) and then add a microversion that doesn't allow it, I was
> half joking, but I see we're on the same page.  This scenario seems to
> introduce a lot of orchestration work that nova shouldn't necessarily
> be in the business of handling.
I tend to agree with this.   I believe the ability to boot from a volume
with source=image was just a convenience thing and shortcut for users. 
As John stated, we know that we have issues with large images and/or
volumes here with timeouts.  If we want to continue to support this,
then the only way to make sure we don't run into timeout issues is to
look into a callback mechanism from Cinder to Nova, but that seems
awfully heavy handed, just to continue to support Nova orchestrating
this.   The good thing about the Nova and Cinder clients/APIs is that
anyone can write a quick python script to do the orchestration
themselves, if we want to deprecate this.  I'm all for deprecating this.

Walt