eg3 removed unnecessary exposed port

eg3/README.md

@@ -22,7 +22,9 @@ In this section, we test frontend container can cross-communicate with backend c
 
 Steps:
 1. Comment out proxy container
-2. frontend has port 80 exposed; backend has port 5000 exposed;
+2. Remove exposed of both containers, as we they don't need expose their ports to outside environment. We just want to test their cross-communication in the same docker network
+   1. port 80 for frontend; 
+   2. port 5000 for backend;
 3. Run `docker compose build` & `docker compose up`
 4. Create a network: `docker network create mynetwork`
 5. Add containers into network

eg3/docker-compose.yaml

@@ -17,13 +17,9 @@ services:
     build: 
       context: ./frontend
       dockerfile: Dockerfile
-    ports:
-      - "80:80" # Uncomment this line if you want to run the frontend container only
 
   backend:
     container_name: backend
     build:
       context: ./backend
-      dockerfile: Dockerfile
-    ports:
-      - "5000:5000" # Uncomment this line if you want to run the backend container only
+      dockerfile: Dockerfile