pkg/srv/srv.go
func GetCluster(serviceScheme, service, name, dns string, apurls types.URLs) ([]string, error) {
	tempName := int(0)
	tcp2ap := make(map[string]url.URL)

	// First, resolve the apurls
	for _, url := range apurls {
		tcpAddr, err := resolveTCPAddr("tcp", url.Host)
		if err != nil {
			return nil, err
		}
		tcp2ap[tcpAddr.String()] = url
	}

	stringParts := []string{}
	updateNodeMap := func(service, scheme string) error {
		_, addrs, err := lookupSRV(service, "tcp", dns)
		if err != nil {
			return err
		}
		for _, srv := range addrs {
			port := fmt.Sprintf("%d", srv.Port)
			host := net.JoinHostPort(srv.Target, port)
			tcpAddr, terr := resolveTCPAddr("tcp", host)
			if terr != nil {
				err = terr
				continue
			}
			n := ""
			url, ok := tcp2ap[tcpAddr.String()]
			if ok {
				n = name
			}
			if n == "" {
				n = fmt.Sprintf("%d", tempName)
				tempName++
			}
			// SRV records have a trailing dot but URL shouldn't.
			shortHost := strings.TrimSuffix(srv.Target, ".")
			urlHost := net.JoinHostPort(shortHost, port)
			if ok && url.Scheme != scheme {
				err = fmt.Errorf("bootstrap at %s from DNS for %s has scheme mismatch with expected peer %s", scheme+"://"+urlHost, service, url.String())
			} else {
				stringParts = append(stringParts, fmt.Sprintf("%s=%s://%s", n, scheme, urlHost))
			}
		}
		if len(stringParts) == 0 {
			return err
		}
		return nil
	}

	err := updateNodeMap(service, serviceScheme)
	if err != nil {
		return nil, fmt.Errorf("error querying DNS SRV records for _%s %s", service, err)
	}
	return stringParts, nil
}
func GetCluster(serviceScheme, service, name, dns string, apurls types.URLs) ([]string, error) {
	tempName := int(0)
	tcp2ap := make(map[string]url.URL)

	// First, resolve the apurls
	for _, url := range apurls {
		tcpAddr, err := resolveTCPAddr("tcp", url.Host)
		if err != nil {
			return nil, err
		}
		tcp2ap[tcpAddr.String()] = url
	}

	stringParts := []string{}
	updateNodeMap := func(service, scheme string) error {
		_, addrs, err := lookupSRV(service, "tcp", dns)
		if err != nil {
			return err
		}
		for _, srv := range addrs {
			port := fmt.Sprintf("%d", srv.Port)
			host := net.JoinHostPort(srv.Target, port)
			tcpAddr, terr := resolveTCPAddr("tcp", host)
			if terr != nil {
				err = terr
				continue
			}
			n := ""
			url, ok := tcp2ap[tcpAddr.String()]
			if ok {
				n = name
			}
			if n == "" {
				n = fmt.Sprintf("%d", tempName)
				tempName++
			}
			// SRV records have a trailing dot but URL shouldn't.
			shortHost := strings.TrimSuffix(srv.Target, ".")
			urlHost := net.JoinHostPort(shortHost, port)
			if ok && url.Scheme != scheme {
				err = fmt.Errorf("bootstrap at %s from DNS for %s has scheme mismatch with expected peer %s", scheme+"://"+urlHost, service, url.String())
			} else {
				stringParts = append(stringParts, fmt.Sprintf("%s=%s://%s", n, scheme, urlHost))
			}
		}
		if len(stringParts) == 0 {
			return err
		}
		return nil
	}

	err := updateNodeMap(service, serviceScheme)
	if err != nil {
		return nil, fmt.Errorf("error querying DNS SRV records for _%s %s", service, err)
	}
	return stringParts, nil
}
// GetCluster gets the cluster information via DNS discovery.
// Also sees each entry as a separate instance.