containerization-and-devops

Class 9 Part 1 - Docker Compose Scaling

Objective

This experiment demonstrates horizontal scaling in Docker Compose using two different approaches:

1. Removing Port Mapping (Internal Scaling Only)
2. Using Port Range Mapping (Multiple External Ports)

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Approach 1: Removing Port Mapping (Internal Scaling)

In this approach, we removed the ports section from the WordPress service. This allows scaling without port conflicts, but WordPress is not directly accessible from the browser.

docker-compose.yml (No Port Mapping)

services:
  mysql:
    image: mysql:8.0
    container_name: class9_mysql
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: wordpress
      MYSQL_USER: wpuser
      MYSQL_PASSWORD: wppass
    volumes:
      - mysql_data:/var/lib/mysql
    networks:
      - wordpress-network

  wordpress:
    image: wordpress:latest
    environment:
      WORDPRESS_DB_HOST: mysql
      WORDPRESS_DB_USER: wpuser
      WORDPRESS_DB_PASSWORD: wppass
      WORDPRESS_DB_NAME: wordpress
    volumes:
      - wp_content:/var/www/html/wp-content
    depends_on:
      - mysql
    networks:
      - wordpress-network

volumes:
  mysql_data:
  wp_content:

networks:
  wordpress-network:

Scaling Command

docker compose up -d --scale wordpress=3

This created:

• class9-wordpress-1
• class9-wordpress-2
• class9-wordpress-3

---

Approach 2: Port Range Mapping

In this approach, we used a port range to allow multiple containers to bind to different host ports.

docker-compose.yml (Port Range Mapping)

services:
  mysql:
    image: mysql:8.0
    container_name: class9_mysql
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: wordpress
      MYSQL_USER: wpuser
      MYSQL_PASSWORD: wppass
    volumes:
      - mysql_data:/var/lib/mysql
    networks:
      - wordpress-network

  wordpress:
    image: wordpress:latest
    ports:
      - "8080-8082:80"
    environment:
      WORDPRESS_DB_HOST: mysql
      WORDPRESS_DB_USER: wpuser
      WORDPRESS_DB_PASSWORD: wppass
      WORDPRESS_DB_NAME: wordpress
    volumes:
      - wp_content:/var/www/html/wp-content
    depends_on:
      - mysql
    networks:
      - wordpress-network

volumes:
  mysql_data:
  wp_content:

networks:
  wordpress-network:

Scaling Command

docker compose up -d --scale wordpress=3

This mapped:

• wordpress-1 → localhost:8080
• wordpress-2 → localhost:8081
• wordpress-3 → localhost:8082

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Screenshots

Screenshot 1

Screenshot 2

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Key Concepts Learned

• Port conflicts occur when scaling with fixed host ports
• Removing ports allows internal-only scaling
• Port range mapping allows multiple external access points
• Horizontal scaling creates multiple container replicas
• Docker Compose uses service names for networking

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Conclusion

The experiment successfully demonstrated two methods of scaling WordPress containers using Docker Compose. Both approaches highlight important differences in how Docker handles port binding and service replication.

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