Ubuntu环境下Docker容器间通信故障排查：Django与Flask服务互访失败问题求助

Let's break down why your Flask container can't reach your Django service and fix it step by step:

Root Cause #

Your two docker-compose projects are creating separate default networks by default, which means the Flask container can't resolve or reach the Django container. Using the host's Docker bridge IP (172.17.0.1) or tools like docker-host won't solve this because the containers aren't in the same network space.

Step 1: Create a Shared Docker Network #

First, create a single external network that both projects will use. Run this command in your terminal:

docker network create ecommerce-shared-network

Step 2: Update Django's docker-compose.yml #

Modify your Django docker-compose.yml to use the shared network instead of its isolated one:

version: '3.8'
services:
  backend:
    build:
      context: .
      dockerfile: Dockerfile
    command: "python manage.py runserver 0.0.0.0:8000"
    ports:
      - 8000:8000
    volumes:
      - .:/app
    depends_on:
      - db
    networks:
      - shared-network
  queue:
    build:
      context: .
      dockerfile: Dockerfile
    command: "python consumer.py"
    depends_on:
      - db
    networks:
      - shared-network
  db:
    image: mysql:5.7.22
    restart: always
    environment:
      MYSQL_DATABASE: admin
      MYSQL_USER: root
      MYSQL_PASSWORD: root
      MYSQL_ROOT_PASSWORD: root
    volumes:
      - .dbdata:/var/lib/mysql
    ports:
      - 33066:3306
    networks:
      - shared-network
  # Remove dockerhost and tcp_message_emitter - they're not needed for cross-container communication

# Replace the old backend network with the shared external network
networks:
  shared-network:
    external: true
    name: ecommerce-shared-network

Step 3: Update Flask's docker-compose.yml #

Add the shared network to your Flask project's docker-compose.yml too:

version: '3.8'
services:
  backend:
    build:
      context: .
      dockerfile: Dockerfile
    command: "python main.py"
    ports:
      - 8001:5000
    volumes:
      - .:/app
    depends_on:
      - db
    networks:
      - shared-network
  queue:
    build:
      context: .
      dockerfile: Dockerfile
    command: "python consumer.py"
    depends_on:
      - db
    networks:
      - shared-network
  db:
    image: mysql:5.7.22
    restart: always
    environment:
      MYSQL_DATABASE: main
      MYSQL_USER: root
      MYSQL_PASSWORD: root
      MYSQL_ROOT_PASSWORD: root
    volumes:
      - .dbdata:/var/lib/mysql
    ports:
      - 33067:3306
    networks:
      - shared-network

# Add the shared network definition
networks:
  shared-network:
    external: true
    name: ecommerce-shared-network

Step 4: Update Flask Code to Use Django's Service Name #

Instead of using the host IP (172.17.0.1), use the service name from Django's docker-compose (backend) as the hostname. Docker's built-in DNS will automatically resolve this to the Django container's IP within the shared network:

@app.route("/api/products/<int:id>/like", methods=["POST"])
def like(id):
    # Replace the hardcoded IP with the Django service name
    req = requests.get("http://backend:8000/api/user")
    json = req.json()
    try:
        product_user = ProductUser(user_id=json["id"], product=id)
        db.session.add(product_user)
        db.session.commit()
        publish("product_liked", id)
    except:
        abort(400, "You already liked this product")
    return jsonify({ "message": "success" })

Why This Works #

• By putting both containers in the same network, they can communicate directly using their service names (no need for host IPs or port forwarding between containers).
• Docker's internal DNS handles resolving service names to container IPs, so you don't have to hardcode dynamic IP addresses.
• The dockerhost tool is designed for containers to reach services running on the host machine, not for container-to-container communication—so we can safely remove it here.

Additional Checks #

• Verify your Django /api/user endpoint is working correctly by testing it directly via http://localhost:8000/api/user first.
• Add healthchecks to your Django service to ensure it's fully ready before Flask tries to connect:

  backend:
    # ... existing config ...
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:8000/api/user"]
      interval: 10s
      timeout: 5s
      retries: 5
  

内容的提问来源于stack exchange，提问作者Luis Batista