Cloned from launchpad blueprint https://blueprints.launchpad.net/nova/+spec/flexible-evacuate-scheduler.

Description:

Currently, we can only evacuate vm to a specified host and also we did not make some pre-checking to see if the host is valid or not.

The bp include two requirements:
1) Enable nova scheduler validate target evacuate host if evacuate with a specified host.
2) Enable nova scheduler help select a best target host for evacuate just like live migration without target host.

For item 1), we can leverage the logic from https://blueprints.launchpad.net/nova/+spec/validate-targethost-live-migration.

For item 2), we may need to add an evacuate task just like live migration task and let evacuate task call nova scheduler select_destinations to select best target host for evacuate if evacuate host was not specified.


Specification URL (additional information):

None