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Hi Sandy,

Thanks for taking the time to read this.

My understanding is that a typical Nova deployment would span across multiple zones, that zones may have subzones, and that child zones will have a number of availability zones in them; please do correct me if I am wrong :)

That stated, it was assumed that an aggregate will be a grouping of servers within an availability zone (hence the introduction of the extra concept), and would be used to manage hypervisor pools when and if required. This introduces benefits like VM live migration, VM HA and zero-downtime host upgrades. The introduction of hypervisor pools is just the easy way to get these benefits in the short term. 

Going back to your point, it is possible to match "host-aggregates" with "single-zone that uses capabilities" on the implementation level (assumed that it is okay to be unable to represent aggregates as children of availability zones). Nevertheless, I still see zones and aggregates as being different on the conceptual level. 

What is your view if we went with the approach of implementing an aggregate as a special "single-zone that uses capabilities"? Would there be a risk of tangling the zone management API a bit?

Thanks for feedback!

Cheers,
Armando

> -----Original Message-----
> From: Sandy Walsh [mailto:sandy.walsh at RACKSPACE.COM]
> Sent: 09 November 2011 21:10
> To: Armando Migliaccio
> Cc: openstack at lists.launchpad.net
> Subject: Host Aggregates ...
> 
> Hi Armando,
> 
> I finally got around to reading
> https://blueprints.launchpad.net/nova/+spec/host-aggregates.
> 
> Perhaps you could elaborate a little on how this differs from host
> capabilities (key-value pairs associated with a service) that the scheduler
> can use when making decisions?
> 
> The distributed scheduler doesn't need zones to operate, but will use them if
> available. Would host-aggregates simply be a single-zone that uses
> capabilities?
> 
> Cheers,
> Sandy