code: func (tc *TeleportClient) getTargetNodes(ctx context.Context, proxy *ProxyClient) ([]string, error) {
  	var (
  		err    error
  		nodes  []services.Server
  		retval = make([]string, 0)
  	)
  	if tc.Labels != nil && len(tc.Labels) > 0 {
  		nodes, err = proxy.FindServersByLabels(ctx, tc.Namespace, tc.Labels)
  		if err != nil {
  			return nil, trace.Wrap(err)
  		}
  		for i := 0; i < len(nodes); i++ {
  			retval = append(retval, nodes[i].GetAddr())
  		}
  	}
  	if len(nodes) == 0 {
  		retval = append(retval, net.JoinHostPort(tc.Host, strconv.Itoa(tc.HostPort)))
  	}
  	return retval, nil
  }
docs: // getTargetNodes returns a list of node addresses this SSH command needs to
  // operate on.