'Return Server\'s Availability Zone.
Fetching it from Nova if necessary.'

def _availability_zone(self):

    availability_zone = self.properties[self.AVAILABILITY_ZONE]
    if (availability_zone is None):
        try:
            server = self.client().servers.get(self.resource_id)
        except Exception as e:
            self.client_plugin().ignore_not_found(e)
            return
    return getattr(server, 'OS-EXT-AZ:availability_zone', None)
