code: func (s *clusterPeer) Dial(params DialParams) (conn net.Conn, err error) {
  	return nil, trace.ConnectionProblem(nil, "unable to dial, this proxy %v has not been discovered yet, try again later", s)
  }
docs: // Dial is used to connect a requesting client (say, tsh) to an SSH server
  // located in a remote connected site, the connection goes through the
  // reverse proxy tunnel.