code: func (r *EtcdRegistry) EngineVersion() (int, error) {
  	res, err := r.kAPI.Get(context.Background(), r.engineVersionPath(), nil)
  	if err != nil {
  		// no big deal, either the cluster is new or is just
  		// upgrading from old unversioned code
  		if isEtcdError(err, etcd.ErrorCodeKeyNotFound) {
  			err = nil
  		}
  		return 0, err
  	}
  
  	return strconv.Atoi(res.Node.Value)
  }
docs: // EngineVersion implements the ClusterRegistry interface