code: protected void startServingRPCServer() {
      try {
        stopRejectingRpcServer();
        LOG.info("Starting gRPC server on address {}", mRpcBindAddress);
        GrpcServerBuilder serverBuilder = GrpcServerBuilder.forAddress(
            mRpcConnectAddress.getHostName(), mRpcBindAddress, ServerConfiguration.global());
        registerServices(serverBuilder, mJobMaster.getServices());
  
        mGrpcServer = serverBuilder.build().start();
        LOG.info("Started gRPC server on address {}", mRpcConnectAddress);
  
        // Wait until the server is shut down.
        mGrpcServer.awaitTermination();
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }
docs: Starts the gRPC server. The AlluxioMaster registers the Services of registered
  {@link Master}s and meta services.