code: func omitHostnameInTranslation(forwardIPs []string) ([]string, error) {
  	index := 0
  	for _, value := range forwardIPs {
  		proxyHost, _, err := kubeadmutil.ParseHostPort(value)
  		if err != nil {
  			return nil, err
  		}
  		parseIP := net.ParseIP(proxyHost)
  		if parseIP == nil {
  			klog.Warningf("your kube-dns configuration contains a hostname %v. It will be omitted in the translation to CoreDNS as hostnames are unsupported", proxyHost)
  		} else {
  			forwardIPs[index] = value
  			index++
  		}
  	}
  	forwardIPs = forwardIPs[:index]
  
  	return forwardIPs, nil
  }
docs: // omitHostnameInTranslation checks if the data extracted from the kube-dns ConfigMap contains a valid
  // IP address. Hostname to nameservers is not supported on CoreDNS and will
  // skip that particular instance, if there is any hostname present.