code: func (a *application) coordinatorClient(host string) (*coordinator.Client, error) {
  	host, err := a.resolveHost(host)
  	if err != nil {
  		return nil, errors.Annotate(err, "").Err()
  	}
  
  	// Get our Coordinator client instance.
  	prpcClient := prpc.Client{
  		C:       a.httpClient,
  		Host:    host,
  		Options: prpc.DefaultOptions(),
  	}
  	prpcClient.Options.Insecure = a.insecure
  	return coordinator.NewClient(&prpcClient), nil
  }
docs: // coordinatorClient returns a Coordinator client for the specified host. If
  // no host is provided, the command-line host will be used.