type CoreDNS struct {
	domainNames []string
	domainIPs   set.StringSet
	domainPort  string
	prefixPath  string
	etcdClient  *clientv3.Client
}

// EtcdOption - functional options pattern style
type EtcdOption func(*CoreDNS)

// DomainNames set a list of domain names used by this CoreDNS
// client setting, note this will fail if set to empty when
// constructor initializes.