code: func (os *OpenStack) InstanceID() (string, error) {
  	if len(os.localInstanceID) == 0 {
  		id, err := readInstanceID(os.metadataOpts.SearchOrder)
  		if err != nil {
  			return "", err
  		}
  		os.localInstanceID = id
  	}
  	return os.localInstanceID, nil
  }
docs: // InstanceID returns the kubelet's cloud provider ID.