DockerLabs Banner

Lab 005 - Docker Compose - WordPress & MariaDB¶

This lab demonstrates how to use Docker Compose to orchestrate a simple multi-container application: WordPress with a MariaDB database backend.

Overview¶

The provided docker-compose.yaml file defines two main services:
- db: Runs a MariaDB database (can be switched to MySQL if desired).
- wordpress: Runs the latest WordPress application, connected to the database.
A named volume db_data is used to persist database data.

docker-compose.yaml Breakdown¶

db service¶

Uses the mariadb:10.6.4-focal image (or optionally MySQL).
Sets up environment variables for root password, database, user, and password.
Persists data in a Docker volume.
Exposes ports 3306 and 33060 (internal only).

wordpress service¶

Uses the latest WordPress image.
Maps port 80 on the host to port 80 in the container.
Configures environment variables to connect to the database.

volumes¶

db_data: Persists MariaDB data between container restarts.

Bonus Demo¶

I prepared a demo of this lab, which you can view on KillerCoda: Portainder Demo.
The demo is showcases for setting and running multuple containers using Docker Compose
The demo is available on KillerCoda.

How to Run the Lab¶

Navigate to the lab directory:
```
cd Labs/005-DockerCompose
```
Start the services:
```
docker compose up -d
```
This will pull the required images (if not already present) and start both the database and WordPress containers in detached mode.
Access WordPress:
Open your browser and go to http://localhost
Complete the WordPress setup wizard.
Stop the services:
```
docker compose down
```
This will stop and remove the containers, but the database data will persist in the db_data volume.

Notes¶

To use MySQL instead of MariaDB, uncomment the relevant line in the compose file and comment out the MariaDB image line.
The database credentials are set for demonstration purposes. For production, use secure passwords.
The db service is only accessible to the wordpress service (not exposed to the host).

Advanced Concepts¶

Docker Compose Networks¶

Docker Compose automatically creates a default network for your services. However, you can define custom networks for better isolation and control:

services:
  wordpress:
    networks:
      - frontend
      - backend

  db:
    networks:
      - backend

networks:
  frontend:
    driver: bridge
  backend:
    driver: bridge
    internal: true  # No external access

Network Types: - bridge: Default network driver for standalone containers - host: Use the host’s network directly - overlay: For multi-host networking (Docker Swarm) - macvlan: Assign MAC addresses to containers - none: Disable networking

Volume Management¶

Named Volumes vs Bind Mounts:

services:
  wordpress:
    volumes:
      # Named volume (managed by Docker)
      - wp_data:/var/www/html

      # Bind mount (host directory)
      - ./my-theme:/var/www/html/wp-content/themes/my-theme

      # Anonymous volume
      - /var/www/html/tmp

volumes:
  wp_data:
    driver: local
    driver_opts:
      type: none
      o: bind
      device: /path/on/host

Volume Best Practices: - Use named volumes for data persistence - Use bind mounts for development (live code updates) - Use anonymous volumes for temporary data - Always backup volumes before major updates

Health Checks¶

Add health checks to ensure services are running correctly:

services:
  wordpress:
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost"]
      interval: 30s
      timeout: 10s
      retries: 3
      start_period: 40s

  db:
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "localhost"]
      interval: 10s
      timeout: 5s
      retries: 5

Resource Limits¶

Control resource allocation to prevent any service from consuming all resources:

services:
  wordpress:
    deploy:
      resources:
        limits:
          cpus: '0.50'
          memory: 512M
        reservations:
          cpus: '0.25'
          memory: 256M

Restart Policies¶

Configure how containers should restart:

services:
  wordpress:
    restart: unless-stopped  # Options: no, always, on-failure, unless-stopped

Dependency Management¶

Control startup order with depends_on:

services:
  wordpress:
    depends_on:
      db:
        condition: service_healthy  # Wait for db to be healthy

Logging Configuration¶

Configure log drivers and options:

services:
  wordpress:
    logging:
      driver: "json-file"
      options:
        max-size: "10m"
        max-file: "3"

Best Practices¶

Use Environment Variables: Store configuration in .env files

# .env file
MYSQL_ROOT_PASSWORD=secure_password
MYSQL_DATABASE=wordpress

Version Your Compose Files: Always specify the Compose version
```
version: '3.8'
```
Use Specific Image Tags: Avoid latest tag in production
```
image: mariadb:10.6.4-focal
```
Organize Services Logically: Group related services
Frontend services
Backend services
Database services
Cache services
Use Multi-Stage Builds: For custom images, use multi-stage Dockerfiles
Implement Health Checks: Always add health checks for critical services

Secure Secrets: Use Docker secrets or external secret management

services:
  db:
    secrets:
      - db_password

secrets:
  db_password:
    file: ./secrets/db_password.txt

Use .dockerignore: Exclude unnecessary files from build context
Network Isolation: Use custom networks to isolate services
Monitor Resources: Set resource limits to prevent resource exhaustion

Useful Docker Compose Commands¶

# View configuration (merged from all compose files)
docker compose config

# Validate compose file
docker compose config --quiet

# Pull all images
docker compose pull

# Build services
docker compose build

# Start services
docker compose up -d

# View running services
docker compose ps

# View logs
docker compose logs -f [service_name]

# Execute command in running container
docker compose exec wordpress bash

# Scale services
docker compose up -d --scale wordpress=3

# Stop services
docker compose stop

# Stop and remove containers
docker compose down

# Stop, remove containers and volumes
docker compose down -v

# Restart services
docker compose restart

# Pause services
docker compose pause

# Unpause services
docker compose unpause

# View resource usage
docker compose top

Troubleshooting¶

If you encounter port conflicts, ensure nothing else is running on port 80.

To view logs for a service:

docker compose logs wordpress
docker compose logs db

Check service health:
```
docker compose ps
```

Inspect network connectivity:

docker network inspect 005-dockercompose_default

Debug startup issues:

docker compose up --no-start
docker compose start

This lab is part of the DockerLabs series. See other labs for more Docker scenarios and hands-on exercises.