Where we are trying to find a good solution is regarding how to use spot market resources in our cloud. If we allocate out a quota to a project but they do not use the full resources, we want to be able to offer that quota to others on a low SLA (killed with little warning). This allows us to get our resource utilisation up while ensuring that projects can get the resources they’re entitled to when there is a need.
This is an interesting area to be getting a few sites together to share solutions.
This is an area I'm looking at as well. My short term desire is to provide a way to provided for the same hardware sometimes being used to run virtualized instances and sometimes be provisioned as a baremetal system (either through Triple0 or manually reprovisioned). My short term solution seems to be evolving around host-aggregates and special flavors.
That communicates the "these can disappear at any time" SLA but doesn't address the quota issue which I think is a more general need. In many deployment resource cost is expressed directly as cost, in my research environment we don't have any direct internal billing for compute resources and I don' t pretend to understand the labyrinth of grants that fund the place, so "cost" here is expressed in quotas. I want people to have large (possibly infinite) quotas for cheap resources like "spot instances" and small quotas for "expensive" resources for example aggregates with 1:1 virtual to physical resource allocation.
I though I remembered talk of abstracting the quota system into it's own project at the Portland summit, but can't seem to find it in my notes or on line, if I didn't dream that I'd love it if someone could refresh my memory.