Docker Expert Skill

Core Principles

Directory Organization (Windows)

Organize all Docker data under a single root directory for maintainability:

C:\Users\{username}\Docker\
├── {service-name}\
│   ├── data\           # Persistent data (databases, media, configs)
│   ├── config\         # Configuration files
│   └── logs\           # Log files (if not using Docker logging)

Docker Compose Best Practices

Always use docker-compose.yml for multi-container setups. Structure:

version: "3.8"

services:
  service-name:
    image: image:tag
    container_name: service-name
    restart: unless-stopped
    ports:
      - "host:container"
    volumes:
      - ./data:/container/path
    environment:
      - VAR_NAME=value
    networks:
      - network-name

networks:
  network-name:
    driver: bridge

Volume Patterns

Named volumes (Docker-managed):

volumes:
  - db-data:/var/lib/postgresql/data
volumes:
  db-data:

Bind mounts (host-managed, preferred for Windows):

volumes:
  - C:/Users/Username/Docker/service/data:/container/path
  # Or relative paths:
  - ./data:/container/path

Common Services Reference

Windows-Specific Notes

1. Path format: Use forward slashes or escaped backslashes in compose files

• ✅ C:/Users/Name/Docker/data
• ✅ C:\\Users\\Name\\Docker\\data
• ❌ C:\Users\Name\Docker\data

1. WSL2 Backend: Recommended for better performance. Enable in Docker Desktop settings.
2. File permissions: Windows volumes don't support Unix permissions; use user: directive when needed
3. Line endings: Ensure .sh scripts use LF, not CRLF

Troubleshooting Commands

# View logs
docker logs -f container-name

# Shell into container
docker exec -it container-name /bin/bash
# Or for Alpine-based:
docker exec -it container-name /bin/sh

# Check resource usage
docker stats

# Inspect container
docker inspect container-name

# Network debugging
docker network ls
docker network inspect network-name

# Clean up
docker system prune -a        # Remove all unused images
docker volume prune           # Remove unused volumes

Migration Workflow

When reorganizing Docker data:

1. Stop containers: docker-compose down
2. Create new directory structure
3. Copy data (preserve permissions where possible)
4. Update docker-compose.yml paths
5. Start containers: docker-compose up -d
6. Verify functionality
7. Remove old directories only after confirmation

Health Checks

Add health checks for critical services:

healthcheck:
  test: ["CMD", "curl", "-f", "http://localhost:8080/health"]
  interval: 30s
  timeout: 10s
  retries: 3
  start_period: 40s

Environment Variables

Use .env file for sensitive data:

# .env file (never commit to git)
DB_PASSWORD=secretpassword
API_KEY=your-api-key

Reference in compose:

environment:
  - DB_PASSWORD=${DB_PASSWORD}

Backup Strategy

For critical data volumes:

# Backup a volume
docker run --rm -v volume-name:/source -v $(pwd):/backup alpine tar czf /backup/backup.tar.gz -C /source .

# Restore a volume
docker run --rm -v volume-name:/target -v $(pwd):/backup alpine tar xzf /backup/backup.tar.gz -C /target

Additional Resources

• Compose examples: See references/compose-examples.md for complete service configurations
• Networking guide: See references/networking.md for advanced network setups