code: func (ins *instance) ping(timeout time.Duration) bool {
  	session, err := mgo.DialWithTimeout(ins.url(), timeout)
  	if err != nil {
  		return false
  	}
  	defer session.Close()
  	session.SetSyncTimeout(timeout)
  	if err = session.Ping(); err != nil {
  		return false
  	}
  	return true
  }
docs: // ping won't work with old (1.2) mongo servers.