code: def start_server(self, addr='', port=8000):
          
          if self._multiprocess_on:
              raise SanicPrometheusError(
                  "start_server can not be used when multiprocessing " +
                  "is turned on")
          start_http_server(addr=addr, port=port)
docs: Expose /metrics endpoint on a new server that will
          be launched on `<addr>:<port>`.
  
          This may be useful if you want to restrict access to
          metrics data with firewall rules.
          NOTE: can not be used in multiprocessing mode