docker-containerization

Docker Containerization Skill

Comprehensive guide for Docker containerization covering core concepts, multi-stage builds, Docker Compose orchestration, development environment setup, and advanced patterns for isolated development workflows.

When to Use This Skill

Use this skill when:

• Containerization: Building Docker images, writing Dockerfiles, multi-stage builds
• Docker Compose: Setting up multi-container applications, local development environments
• Development Environments: Setting up DDEV for TYPO3/PHP projects, creating isolated worktrees
• Container Optimization: Analyzing and optimizing Dockerfile efficiency, image size reduction
• Port Management: Allocating ports for multiple containers, avoiding conflicts
• Browser Automation: Setting up isolated browser containers for testing
• CI/CD: Building container images for deployment pipelines
• Meta-Configuration Systems: Working with meta.json-driven Docker configurations (Ghostmind)

Quick Start

Basic Docker Workflow

# Create Dockerfile
cat > Dockerfile <<EOF
FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --production
COPY . .
EXPOSE 3000
USER node
CMD ["node", "server.js"]
EOF

# Build and run
docker build -t myapp:1.0 .
docker run -d -p 3000:3000 --name myapp myapp:1.0

See: references/docker-basics.md

Docker Compose Multi-Container App

# docker-compose.yml
version: '3.8'
services:
  web:
    build: .
    ports:
      - "3000:3000"
    depends_on:
      - db
      - redis
    environment:
      - DATABASE_URL=postgresql://user:pass@db:5432/app

  db:
    image: postgres:15-alpine
    volumes:
      - postgres_data:/var/lib/postgresql/data

  redis:
    image: redis:7-alpine

volumes:
  postgres_data:

See: references/docker-compose.md

Core Docker Concepts

Dockerfile Best Practices

# Use specific versions (not latest)
FROM node:20.11.0-alpine3.19

# Set working directory
WORKDIR /app

# Copy dependency files first (better caching)
COPY package*.json ./
RUN npm ci --only=production

# Copy application code
COPY . .

# Set environment variables
ENV NODE_ENV=production

# Document exposed ports
EXPOSE 3000

# Create and use non-root user (security)
RUN addgroup -g 1001 -S nodejs && \
    adduser -S nodejs -u 1001
USER nodejs

# Default command
CMD ["node", "server.js"]

Multi-Stage Builds

# Stage 1: Build
FROM node:20-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Stage 2: Production (smaller image)
FROM node:20-alpine
WORKDIR /app
COPY --from=build /app/dist ./dist
COPY --from=build /app/node_modules ./node_modules
USER node
EXPOSE 3000
CMD ["node", "dist/server.js"]

Benefits: Smaller images, improved security, no build tools in production.

.dockerignore

node_modules
.git
.env
*.log
.DS_Store
README.md
docker-compose.yml
dist
coverage

Best Practices

Dockerfiles

• Use specific image versions, not latest
• Run as non-root user
• Multi-stage builds to minimize size
• Implement health checks
• Set resource limits
• Keep images under 500MB
• Scan for vulnerabilities regularly

Docker Compose

• Use named volumes for data persistence
• Implement health checks for all services
• Set restart policies for production
• Use environment-specific compose files
• Configure resource limits
• Enable logging with size limits
• Network isolation with custom networks

Development Environments

• Use consistent port allocation across worktrees
• Isolate browser state for parallel testing
• Copy .env files when creating worktrees
• Configure CORS for worktree frontend ports
• Stop services when not in use

Quick Reference

Task	Command
Build	docker build -t myapp:1.0 .
Run	docker run -d -p 8080:3000 myapp:1.0
Logs	docker logs -f myapp
Shell	docker exec -it myapp /bin/sh
Stop	docker stop myapp
Remove	docker rm myapp
Compose up	docker compose up -d
Compose down	docker compose down
Clean all	docker system prune -a --volumes

See Extended Patterns for Docker Compose patterns, DDEV setup, worktree isolation, container optimization, CI/CD pipelines, and troubleshooting.

Reference Navigation

Topic	Reference File
Docker basics and Dockerfile	references/docker-basics.md
Docker Compose orchestration	references/docker-compose.md
Extended patterns and examples	references/extended-patterns.md
Ghostmind meta.json config	references/docker-meta-config.md
Worktree Docker strategy	references/docker-worktree-strategy.md
Port allocation	references/port-allocation.md
Browser isolation	references/browser-isolation.md
CORS configuration	references/cors-configuration.md
Docker troubleshooting	references/docker-troubleshooting.md
DDEV quickstart	references/ddev-quickstart.md
DDEV advanced options	references/ddev-advanced-options.md
DDEV prerequisites	references/ddev-prerequisites.md
DDEV troubleshooting	references/ddev-troubleshooting.md

Scripts Reference

Script	Purpose
scripts/docker_optimize.py	Analyze and optimize Dockerfiles
scripts/validate-prerequisites.sh	Check Docker, DDEV installation
scripts/worktree-manager.sh	Manage isolated worktree environments
scripts/setup-mcp-isolation.sh	Configure browser MCP isolation
scripts/validate-worktree-connectivity.sh	Test worktree service connectivity
scripts/test-isolation.sh	Test browser isolation
scripts/migrate-browser-isolation.sh	Migrate to new isolation config

Resources

• Docker Docs: https://docs.docker.com
• Docker Compose: https://docs.docker.com/compose/
• Dockerfile Reference: https://docs.docker.com/engine/reference/builder/
• DDEV: https://ddev.readthedocs.io/
• Docker Security: https://docs.docker.com/engine/security/