code: func translateUpstreamNameServerOfKubeDNSToUpstreamForwardCoreDNS(dataField string, kubeDNSConfigMap *v1.ConfigMap) (string, error) {
  	if kubeDNSConfigMap == nil {
  		return "", nil
  	}
  
  	if upstreamValues, ok := kubeDNSConfigMap.Data[dataField]; ok {
  		var upstreamProxyValues []string
  
  		err := json.Unmarshal([]byte(upstreamValues), &upstreamProxyValues)
  		if err != nil {
  			return "", errors.Wrap(err, "failed to parse JSON from 'kube-dns ConfigMap")
  		}
  
  		upstreamProxyValues, err = omitHostnameInTranslation(upstreamProxyValues)
  		if err != nil {
  			return "", errors.Wrap(err, "invalid format to parse for proxy")
  		}
  
  		coreDNSProxyStanzaList := strings.Join(upstreamProxyValues, " ")
  		return coreDNSProxyStanzaList, nil
  	}
  	return "/etc/resolv.conf", nil
  }
docs: // translateUpstreamNameServerOfKubeDNSToUpstreamForwardCoreDNS translates UpstreamNameServer Data in kube-dns ConfigMap
  // in the form of Proxy for the CoreDNS Corefile.