class_docstr: GRPCServer
code: def start(self, host: str, port: int):
      uri = str(host) + ":" + str(port)
      self._server.add_insecure_port(uri)
      self._server.start()
      engine_log.info("Start grpc server at %s.", uri)
  
imports: import typing
  import inspect
  import traceback
  from concurrent import futures
  from towhee.utils.thirdparty.grpc_utils import grpc
  from .None import service_pb2
  from .None import service_pb2_grpc
  from towhee.serve.io import JSON, TEXT, BYTES, NDARRAY
  from towhee.serve.api_service import RouterConfig
  from towhee.utils.log import engine_log
label_desc: Use image node_id 2 for calling the GRPCServer obj's underlying member method code with example usage: obj.start(host, port) without return types