def setup_unit_change(self, unit_name, instance, change="joined"):
if instance is None:
unit_data = {}
else:
unit_data = {'private-address': instance.private_ip_address}
unit = self.get_unit(
unit_name,
{unit_name: unit_data},
instance=instance)
controller = Controller(unit)
getattr(controller, "on_%s" % change)()
config = unit.config_get()
return controller.get_hostname(config)
