With Grizzly came the instance evacuation but a quite recent addition to the code expended it to hosts.

With the help of the nova evacuate command you can easily migrate a VM from a dead compute. Now with the nova host-evacuate all the instances from a dead compute can be moved to a new host:

• either specified from the command
• either chosen by the nova scheduler

Usage:

$ nova host-evacuate [--target_host <target_host>] [--on-shared-storage] <host>

Evacuate all instances from failed host to specified one.

Optional arguments:

• --target_host <target_host>: Name of target host.
• --on-shared-storage: Specifies whether all instances files are on share storage

The implementation is a good idea but ideally I’d rather prefer to get a balanced relocation of all the VMs instead of having a new compute. Since all the computes might be evenly loaded, we could end up in a situation where no valid host can be found.