[openstack-dev] Next steps for Whole Host allocation / Pclouds

Jay Pipes jaypipes at gmail.com
Wed Jan 22 01:50:36 UTC 2014

On Tue, 2014-01-21 at 14:28 +0000, Day, Phil wrote:
> > >
> > > I think there is clear water between this and the existing aggregate based
> > isolation.  I also think this is a different use case from reservations.   It's
> > *mostly* like a new scheduler hint, but because it has billing impacts I think it
> > needs to be more than just that - for example the ability to request a
> > dedicated instance is something that should be controlled by a specific role.
> > >
> > 
> > I agree with that, that's another scheduler filter with extra scheduler hint,
> > plus a notification message on the AMQP queue thanks to an handler. That's
> > not role of Nova but Ceilometer to handle billable items and meters
> > consolidation.
> > That said, AWS dedicated instances are backed by VPC, so that's not fairly
> > identical from what you propose here. Here the proposal is more likely
> > making me thinking of AWS "reserved" instances without a contractual
> > period.
> > 
> > IMHO, this model is interesting but hard to use for operators, because they
> > don't have visibility on the capacity. Anyway, if Nova would provide this
> > feature, Climate would be glad using it (and on a personal note, I would be
> > glad contributing to it).
> > 
> I think VPC in AWS is more of a network construct that anything to do with specific hosts - (i.e the difference between running nova-net or neutron in flat mode vs vlan or vxlan mode).

That is correct. VPC is about network isolation, not host isolation. At
least, that is how I understand the AWS VPC docs.

> I agree that it is hard for an operator to work out how to charge for this - in effect it comes down to some sort of statistical model to work out what additional premium you need to charge to recover the cost of the capacity that is now not usable by other tenants.   This kind of thing becomes easier at scale than it is for very small systems.   So some/many operators may decide that they don't want to offer it (which is why it needs to be a specific feature in my mind, even if that does mean a minor bump to the API version in V3 and a new extension to provide the new option in V2 - sorry Jay).   It probably even merits its own specific quota value (max number of dedicated instances).   I'm not sure that its really that much harder to manage than any other capacity issue though - for example if you define a flavor that occupies 

Yup, agreed. It's difficult to guess what the capacity implications
would be without having solid numbers on customer demands for this
functionality, including hard data on how long such instances would
typically live (see my previous point about re-using compute hosts for
other purposes once the last dedicated instance is terminated on that


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