code: async def roll_call_handler(service, action_type, payload, props, **kwds):
      
      # if the action type corresponds to a roll call
      if action_type == roll_call_type():
          # then announce the service
          await service.announce()
docs: This action handler responds to the "roll call" emitted by the api
          gateway when it is brought up with the normal summary produced by
          the service.