Module 8: Docker Compose Advanced

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So far, you’ve learned how to use Docker Compose to define and run multi-container applications. In this module, we’ll go deeper into advanced features that make Compose powerful for real-world projects.

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🔹 1. Environment Variables in docker-compose.yml

Instead of hardcoding values in your Compose file, you can use environment variables for flexibility and security.

👉 Example: .env file

MYSQL_ROOT_PASSWORD=secret123
MYSQL_DATABASE=mydb

👉 Example: docker-compose.yml

version: "3.9"
services:
  db:
    image: mysql:8
    environment:
      - MYSQL_ROOT_PASSWORD=${MYSQL_ROOT_PASSWORD}
      - MYSQL_DATABASE=${MYSQL_DATABASE}

✅ This way, sensitive data (like passwords) stays outside your codebase.

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🔹 2. Scaling Services

You can run multiple instances of a service using the --scale flag. This is useful for scaling apps in development.

👉 Example:

docker-compose up --scale web=3 -d

This will create 3 containers for the web service, all connected to the same network.

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🔹 3. Using Profiles in Docker Compose

Profiles allow you to define optional services that should only run in specific scenarios.

👉 Example: docker-compose.yml

version: "3.9"
services:
  app:
    image: myapp:latest
    ports:
      - "8080:8080"

  db:
    image: postgres:14
    profiles: ["dev"]

  redis:
    image: redis:7
    profiles: ["cache"]

👉 Run with profiles:

docker-compose --profile dev up
docker-compose --profile cache up

✅ This helps separate development, testing, and production environments.

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🔹 4. Networking with Docker Compose

By default, Docker Compose creates a network so services can communicate by name.

👉 Example:

version: "3.9"
services:
  web:
    image: nginx
    ports:
      - "80:80"
    networks:
      - mynet

  api:
    image: myapi:latest
    networks:
      - mynet

networks:
  mynet:

✅ Now, web can reach api using http://api:port.

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🎯 Wrap Up

In this module, you learned how to:

• Use environment variables in Compose files

• Scale services with --scale

• Enable/disable services using profiles

• Manage networks with Docker Compose

With these skills, you can manage flexible, scalable, and environment-specific setups in your projects.

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