For full details on this, see the IRC conversation [1]. tl;dr: the nova compute manager and xen virt driver assume that you can reboot a rescued instance [2] but the API does not allow that [3] and as far as I can tell, it never has. I can only assume that Rackspace had an out of tree change to the API to allow rebooting a rescued instance. I don't know why that wouldn't have been upstreamed, but the upstream API doesn't allow it. I'm also not aware of anything internal to nova that reboots an instance in a rescued state. So the question now is, should we add rescue to the possible states to reboot an instance in the API? Or just rollback this essentially dead code in the compute manager and xen virt driver? I don't know if any other virt drivers will support rebooting a rescued instance. [1] http://eavesdrop.openstack.org/irclogs/%23openstack-nova/%23openstack-nova.2018-05-03.log.html#t2018-05-03T18:49:58 [2] https://review.openstack.org/#/q/topic:bug/1170237+(status:open+OR+status:merged [3] https://github.com/openstack/nova/blob/4b0d0ea9f18139d58103a520a6a4e9119e19a4de/nova/compute/vm_states.py#L69-L72 -- Thanks, Matt