==> /var/log/nova/nova-conductor.log <==
2015-01-28 23:06:06.873 16079 WARNING nova.scheduler.utils [req-8e7b52df-b0d6-486b-9629-7ffa6c8b5533 None] Failed to compute_task_migrate_server: No valid host was found.
Traceback (most recent call last):

  File "/usr/lib/python2.7/site-packages/oslo/messaging/rpc/server.py", line 139, in inner
    return func(*args, **kwargs)

  File "/usr/lib/python2.7/site-packages/nova/scheduler/manager.py", line 175, in select_destinations
    filter_properties)

  File "/usr/lib/python2.7/site-packages/nova/scheduler/filter_scheduler.py", line 151, in select_destinations
    raise exception.NoValidHost(reason='')

NoValidHost: No valid host was found.