code: func (a *Agent) JoinWAN(addrs []string) (n int, err error) {
  	a.logger.Printf("[INFO] agent: (WAN) joining: %v", addrs)
  	if srv, ok := a.delegate.(*consul.Server); ok {
  		n, err = srv.JoinWAN(addrs)
  	} else {
  		err = fmt.Errorf("Must be a server to join WAN cluster")
  	}
  	a.logger.Printf("[INFO] agent: (WAN) joined: %d Err: %v", n, err)
  	return
  }
docs: // JoinWAN is used to have the agent join a WAN cluster