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