// constructor initializes.
func DomainNames(domainNames []string) EtcdOption {
	return func(args *CoreDNS) {
		args.domainNames = domainNames
	}
}

// DomainIPs set a list of custom domain IPs, note this will
// fail if set to empty when constructor initializes.
func DomainIPs(domainIPs set.StringSet) EtcdOption {
	return func(args *CoreDNS) {
		args.domainIPs = domainIPs
	}
}