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.wa...@rackspace.com]
> Sent: 09 November 2011 21:10
> To: Armando Migliaccio
> Cc: openstack@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

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