Correct node acknowledgement

SymphonyDiscovery/src/main/java/io/github/lumijiez/JavalinConfig.java

@@ -2,11 +2,34 @@ package io.github.lumijiez;
 
 import com.google.gson.Gson;
 import io.javalin.Javalin;
+import io.javalin.json.JavalinGson;
+import io.javalin.websocket.WsContext;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 public class JavalinConfig {
-    public static Gson gson = new Gson();
+    private static final Map<String, WsContext> users = new ConcurrentHashMap<>();
 
     public static void setup(Javalin app) {
         app.get("/check", ctx -> ctx.result("OK"));
+
+        app.ws("/discovery", ws -> {
+           ws.onConnect(ctx -> {
+               String id = ctx.sessionId();
+               users.put(id, ctx);
+               broadcast("Discovery", "Join");
+           });
+
+           ws.onClose(ctx -> {
+               String id = ctx.sessionId();
+               users.remove(id);
+               broadcast("Discovery", "Leave");
+           });
+        });
+    }
+
+    private static void broadcast(String sender, String message) {
+        users.values().forEach(ctx -> ctx.send(users.size()));
     }
 }

SymphonyDiscovery/src/main/java/io/github/lumijiez/Main.java

@@ -1,10 +1,14 @@
 package io.github.lumijiez;
 
 import io.javalin.Javalin;
+import io.javalin.json.JavalinGson;
 
 public class Main {
     public static void main(String[] args) {
-        Javalin app = Javalin.create().start(8083);
+        Javalin app = Javalin.create(config -> {
+            config.jsonMapper(new JavalinGson());
+        }).start(8083);
+
         JavalinConfig.setup(app);
 
         System.out.print("Discovery service up and running");