Resolver

Resolve API endpoint and cli command return list of hostnames
base on given label.

client/main.go

@@ -114,6 +114,31 @@ func (l *LobbyClient) GetDiscoveries() ([]server.Discovery, error) {
 	return discoveries, nil
 }
 
+// Resolve returns list of hostnames that have given label
+func (l *LobbyClient) Resolve(label server.Label) ([]string, error) {
+	l.init()
+
+	path := fmt.Sprintf("/v1/resolve?label=%s", label.String())
+	method := "GET"
+
+	var hostnames []string
+
+	status, body, err := l.call(method, path, "")
+	if err != nil {
+		return hostnames, err
+	}
+	if status != 200 {
+		return hostnames, fmt.Errorf("non-200 response: %s", body)
+	}
+
+	err = json.Unmarshal([]byte(body), &hostnames)
+	if err != nil {
+		return hostnames, fmt.Errorf("response parsing error: %v", err)
+	}
+
+	return hostnames, nil
+}
+
 // Find discoveries by their labels
 func (l *LobbyClient) FindByLabels(labels server.Labels) ([]server.Discovery, error) {
 	l.init()

ctl/main.go

@@ -14,6 +14,7 @@ func Usage() {
 	flag.Usage()
 	fmt.Println("")
 	fmt.Println("Commands:")
+	fmt.Println("  resolve label                    returns list of hostnames with given label")
 	fmt.Println("  discovery                        returns discovery packet of the server where the client is connected to")
 	fmt.Println("  discoveries                      returns list of all registered discovery packets")
 	fmt.Println("  discoveries labels [LABEL] ...   returns list of all registered discovery packets with given labels (OR)")
@@ -68,6 +69,25 @@ func main() {
 	}
 
 	switch flag.Args()[0] {
+	case "resolve":
+		if len(flag.Args()) == 2 {
+			hostnames, err := client.Resolve(server.Label(flag.Arg(1)))
+			if err != nil {
+				fmt.Println(err)
+				os.Exit(1)
+			}
+			if *jsonOutput {
+				printJSON(hostnames)
+			} else {
+				for _, hostname := range hostnames {
+					fmt.Println(hostname)
+				}
+			}
+		} else {
+			Usage()
+			os.Exit(0)
+		}
+
 	case "discoveries":
 		var discoveries []server.Discovery
 		var err error

daemon/handlers.go

@@ -28,6 +28,20 @@ func listHandler(c echo.Context) error {
 	return c.JSONPretty(200, discoveries, "  ")
 }
 
+// resolveHandler returns hostname(s) based on another label
+func resolveHandler(c echo.Context) error {
+	label := c.QueryParam("label") // This is label we will use to filter discovery packets
+
+	output := []string{}
+
+	discoveries := discoveryStorage.Filter([]string{label})
+	for _, discovery := range discoveries {
+		output = append(output, discovery.Hostname)
+	}
+
+	return c.JSONPretty(http.StatusOK, output, "  ")
+}
+
 func prometheusHandler(c echo.Context) error {
 	name := c.Param("name")
 

daemon/main.go

@@ -204,7 +204,6 @@ func main() {
 	if err != nil {
 		log.Printf("discovery changed error: %v", err)
 	}
-
 	// If config.Register is false this instance won't be registered with other nodes
 	if config.Register {
 		// This is background process that sends the message
@@ -225,7 +224,6 @@ func main() {
 	} else {
 		log.Println("standalone mode, I won't register myself")
 	}
-
 	// --------
 	// REST API
 	// --------
@@ -237,10 +235,10 @@ func main() {
 	}
 	e.Use(middleware.Logger())
 	e.Use(middleware.Recover())
-
 	// Routes
 	if !config.DisableAPI {
 		e.GET("/", listHandler)
+		e.GET("/v1/resolve", resolveHandler)
 		e.GET("/v1/discovery", getIdentificationHandler)
 		e.GET("/v1/discoveries", listHandler)
 		e.POST("/v1/labels", addLabelsHandler)
@@ -251,7 +249,6 @@ func main() {
 	// ------------------------------
 	// Termination signals processing
 	// ------------------------------
-
 	signals := make(chan os.Signal, 1)
 	signal.Notify(signals, syscall.SIGINT, syscall.SIGTERM)
 
@@ -267,7 +264,6 @@ func main() {
 		}
 		e.Shutdown(context.TODO())
 	}(e, config)
-
 	// Start server
 	// In most cases this will end expectedly so it doesn't make sense to use the echo's approach to treat this message as an error.
 	e.Logger.Info(e.Start(config.Host + ":" + strconv.Itoa(int(config.Port))))

daemon/prometheus.go

@@ -39,7 +39,7 @@ func preparePrometheusOutput(name string, discoveries []server.Discovery) Promet
 
 		labels := map[string]string{}
 
-		for _, label := range discovery.FindLabels("prometheus:" + name + ":") {
+		for _, label := range discovery.FindLabelsByPrefix("prometheus:" + name + ":") {
 			trimmed := strings.TrimPrefix(label.String(), "prometheus:"+name+":")
 			parts := strings.SplitN(trimmed, ":", 2)
 			if len(parts) == 2 {

daemon/update.go

@@ -95,6 +95,8 @@ func discoveryChangeLoop() {
 // packet is somehow different than the localone. This can be used to trigger
 // some action in the local machine.
 func discoveryChange(discovery server.Discovery) error {
-	changeDetectedChannel <- true
+	if len(config.Callback) > 0 {
+		changeDetectedChannel <- true
+	}
 	return nil
 }

server/discovery.go

@@ -45,9 +45,9 @@ func (d *Discovery) Bytes() ([]byte, error) {
 	return data, err
 }
 
-// FindLabels returns list of labels with given prefix. For example "service:ns" has prefix "service" or "service:".
+// FindLabelsByPrefix returns list of labels with given prefix. For example "service:ns" has prefix "service" or "service:".
 // It doesn't have to be prefix, but for example "service:test" will match "service:test" and also "service:test2".
-func (d *Discovery) FindLabels(prefix string) Labels {
+func (d *Discovery) FindLabelsByPrefix(prefix string) Labels {
 	labels := Labels{}
 	for _, label := range d.Labels {
 		if strings.HasPrefix(label.String(), prefix) {

server/discovery_test.go

@@ -27,7 +27,7 @@ func TestDiscovery(t *testing.T) {
 	assert.False(t, discovery.IsAlive(), "discovery not suppose to be alive")
 	discovery.LastCheck = now
 
-	assert.Equal(t, Labels{Label("service:test")}, discovery.FindLabels("service"))
+	assert.Equal(t, Labels{Label("service:test")}, discovery.FindLabelsByPrefix("service"))
 	assert.Equal(t, nil, discovery.Validate()) // TODO: This needs more love
 
 	content, err := json.Marshal(&discovery)