docker-patterns

name docker-patterns description Docker and Docker Compose patterns for local development, container security, networking, volume strategies, and multi-service orchestration. Use when setting up containerized development environments or reviewing Docker configurations. metadata {"origin":"ECC"} Docker Patterns Docker and Docker Compose best practices for containerized development. When to Activate Setting up Docker Compose for local development Designing multi-container architectures Troubleshooting container networking or volume issues Reviewing Dockerfiles for security and size Migrating from local dev to containerized workflow Docker Compose for Local Development Standard Web App Stack # docker-compose.yml services: app: build: context: . target: dev # Use dev stage of multi-stage Dockerfile ports: - "3000:3000" volumes: - .:/app # Bind mount for hot reload - /app/node_modules # Anonymous volume -- preserves container deps environment: - DATABASE_URL=postgres://postgres:postgres@db:5432/app_dev - REDIS_URL=redis://redis:6379/0 - NODE_ENV=development depends_on: db: condition: service_healthy redis: condition: service_started command: npm run dev db: image: postgres:16-alpine ports: - "5432:5432" environment: POSTGRES_USER: postgres POSTGRES_PASSWORD: postgres POSTGRES_DB: app_dev volumes: - pgdata:/var/lib/postgresql/data - ./scripts/init-db.sql:/docker-entrypoint-initdb.d/init.sql healthcheck: test: [ "CMD-SHELL" , "pg_isready -U postgres" ] interval: 5s timeout: 3s retries: 5 redis: image: redis:7-alpine ports: - "6379:6379" volumes: - redisdata:/data mailpit: # Local email testing image: axllent/mailpit ports: - "8025:8025" # Web UI - "1025:1025" # SMTP volumes: pgdata: redisdata: Development vs Production Dockerfile # Stage: dependencies FROM node:22-alpine AS deps WORKDIR /app COPY package.json package-lock.json ./ RUN npm ci # Stage: dev (hot reload, debug tools) FROM node:22-alpine AS dev WORKDIR /app COPY --from=deps /app/node_modules ./node_modules COPY . . EXPOSE 3000 CMD ["npm", "run", "dev"] # Stage: build FROM node:22-alpine AS build WORKDIR /app COPY --from=deps /app/node_modules ./node_modules COPY . . RUN npm run build && npm prune --production # Stage: production (minimal image) FROM node:22-alpine AS production WORKDIR /app RUN addgroup -g 1001 -S appgroup && adduser -S appuser -u 1001 USER appuser COPY --from=build --chown=appuser:appgroup /app/dist ./dist COPY --from=build --chown=appuser:appgroup /app/node_modules ./node_modules COPY --from=build --chown=appuser:appgroup /app/package.json ./ ENV NODE_ENV=production EXPOSE 3000 HEALTHCHECK --interval=30s --timeout=3s CMD wget -qO- http://localhost:3000/health || exit 1 CMD ["node", "dist/server.js"] Override Files # docker-compose.override.yml (auto-loaded, dev-only settings) services: app: environment: - DEBUG=app:* - LOG_LEVEL=debug ports: - "9229:9229" # Node.js debugger # docker-compose.prod.yml (explicit for production) services: app: build: target: production restart: always deploy: resources: limits: cpus: "1.0" memory: 512M # Development (auto-loads override) docker compose up # Production docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d Networking Service Discovery Services in the same Compose network resolve by service name: # From "app" container: postgres://postgres:postgres@db:5432/app_dev # "db" resolves to the db container redis://redis:6379/0 # "redis" resolves to the redis container Custom Networks services: frontend: networks: - frontend-net api: networks: - frontend-net - backend-net db: networks: - backend-net # Only reachable from api, not frontend networks: frontend-net: backend-net: Exposing Only What's Needed services: db: ports: - "127.0.0.1:5432:5432" # Only accessible from host, not network # Omit ports entirely in production -- accessible only within Docker network Volume Strategies volumes: # Named volume: persists across container restarts, managed by Docker pgdata: # Bind mount: maps host directory into container (for development) # - ./src:/app/src # Anonymous volume: preserves container-generated content from bind mount override # - /app/node_modules Common Patterns services: app: volumes: - .:/app # Source code (bind mount for hot reload) - /app/node_modules # Protect container's node_modules from host - /app/.next # Protect build cache db: volumes: - pgdata:/var/lib/postgresql/data # Persistent data - ./scripts/init.sql:/docker-entrypoint-initdb.d/init.sql # Init scripts Container Security Dockerfile Hardening # 1. Use specific tags (never :latest) FROM node:22.12-alpine3.20 # 2. Run as non-root RUN addgroup -g 1001 -S app && adduser -S app -u 1001 USER app # 3. Drop capabilities (in compose) # 4. Read-only root filesystem where possible # 5. No secrets in image layers Compose Security services: app: security_opt: - no -new-privileges:true read_only: true tmpfs: - /tmp - /app/.cache cap_drop: - ALL cap_add: - NET_BIND_SERVICE # Only if binding to ports < 1024 Secret Management # GOOD: Use environment variables (injected at runtime) services: app: env_file: - .env # Never commit .env to git environment: - API_KEY # Inherits from host environment # GOOD: Docker secrets (Swarm mode) secrets: db_password: file: ./secrets/db_password.txt services: db: secrets: - db_password # BAD: Hardcoded in image # ENV API_KEY=sk-proj-xxxxx # NEVER DO THIS .dockerignore node_modules .git .env .env.* dist coverage *.log .next .cache docker-compose*.yml Dockerfile* README.md tests/ Debugging Common Commands # View logs docker compose logs -f app # Follow app logs docker compose logs -- tail =50 db # Last 50 lines from db # Execute commands in running container docker compose exec app sh # Shell into app docker compose exec db psql -U postgres # Connect to postgres # Inspect docker compose ps # Running services docker compose top # Processes in each container docker stats # Resource usage # Rebuild docker compose up --build # Rebuild images docker compose build --no-cache app # Force full rebuild # Clean up docker compose down # Stop and remove containers docker compose down -v # Also remove volumes (DESTRUCTIVE) docker system prune # Remove unused images/containers Debugging Network Issues # Check DNS resolution inside container docker compose exec app nslookup db # Check connectivity docker compose exec app wget -qO- http://api:3000/health # Inspect network docker network ls docker network inspect <project>_default Anti-Patterns # BAD: Using docker compose in production without orchestration # Use Kubernetes, ECS, or Docker Swarm for production multi-container workloads # BAD: Storing data in containers without volumes # Containers are ephemeral -- all data lost on restart without volumes # BAD: Running as root # Always create and use a non-root user # BAD: Using :latest tag # Pin to specific versions for reproducible builds # BAD: One giant container with all services # Separate concerns: one process per container # BAD: Putting secrets in docker-compose.yml # Use .env files (gitignored) or Docker secrets When to Use This Skill Setting up Docker Compose for local development Designing multi-container architectures Troubleshooting container issues Reviewing Dockerfiles for security Implementing container best practices