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 ``yaml # 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 `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 `yaml # 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 ` `bash # 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 `yaml 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 `yaml 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 `yaml 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 ``yaml services: app: volumes: - .:/app