Use case is the following:

Compute Node X is running a VM called foo
Compute Node dies (hardware failure, etc)

The datacenter admin might perform manual fencing of the physical node by toggling the power switch off or pulling the plug on it

But we need a way for the admin to tell Nova that "this compute node is now dead, I've manually fenced it".

That API should also then cascade and for every VM that was marked as running on that node, they should all be moved into the down state, since the host was confirmed as being shut off.  This would be an admin level API

There may be some existing APIs on the way in Havana that are close to providing this functionality.  ndipanov will do some investigation to see if any are close or do what is needed.  If not, a new blueprint or modification to an existing blueprint might be needed