code: func appendDNSConfig(existingDNSConfig *runtimeapi.DNSConfig, dnsConfig *v1.PodDNSConfig) *runtimeapi.DNSConfig {
  	existingDNSConfig.Servers = omitDuplicates(append(existingDNSConfig.Servers, dnsConfig.Nameservers...))
  	existingDNSConfig.Searches = omitDuplicates(append(existingDNSConfig.Searches, dnsConfig.Searches...))
  	existingDNSConfig.Options = mergeDNSOptions(existingDNSConfig.Options, dnsConfig.Options)
  	return existingDNSConfig
  }
docs: // appendDNSConfig appends DNS servers, search paths and options given by
  // PodDNSConfig to the existing DNS config. Duplicated entries will be merged.
  // This assumes existingDNSConfig and dnsConfig are not nil.