code: func GetZoneKey(node *v1.Node) string {
  	labels := node.Labels
  	if labels == nil {
  		return ""
  	}
  
  	region, _ := labels[v1.LabelZoneRegion]
  	failureDomain, _ := labels[v1.LabelZoneFailureDomain]
  
  	if region == "" && failureDomain == "" {
  		return ""
  	}
  
  	// We include the null character just in case region or failureDomain has a colon
  	// (We do assume there's no null characters in a region or failureDomain)
  	// As a nice side-benefit, the null character is not printed by fmt.Print or glog
  	return region + ":\x00:" + failureDomain
  }
docs: // GetZoneKey is a helper function that builds a string identifier that is unique per failure-zone;
  // it returns empty-string for no zone.