---
upgrade:
  - |
    A new online data migration has been added to populate missing
    instance.availability_zone values for instances older than Pike whose
    availability_zone was not specified during boot time. This can be run
    during the normal ``nova-manage db online_data_migrations`` routine.
    This fixes `Bug 1768876`_

    .. _Bug 1768876: https://bugs.launchpad.net/nova/+bug/1768876
