One command to spin up a dev environment identical to production dependencies (databases, caches, queues). 2. Core Concepts | Concept | Description | |---------|-------------| | Service | A containerized application (e.g., web app, database) | | Network | Isolated communication layer between services | | Volume | Persistent data storage (survives container restarts) | Default behavior: All services in the same Compose project automatically join a default network and can reach each other using their service name as hostname. 3. The docker-compose.yml File – Anatomy version: '3.8' # Latest stable version (March 2025) services: app: build: ./app ports: - "3000:3000" environment: - NODE_ENV=development depends_on: - db - redis
project/ ├── docker-compose.yml ├── app/ │ ├── Dockerfile │ └── index.js └── .env
build --no-cache # Rebuild images pull # Pull latest images push # Push built images a developer's essential guide to docker compose pdf
services: app: depends_on: db: condition: service_healthy db: image: postgres healthcheck: test: ["CMD-SHELL", "pg_isready -U postgres"] interval: 5s retries: 5
redis: image: redis:alpine ports: - "6379:6379" One command to spin up a dev environment
docker run ... (20 flags) docker network create ... docker volume create ... → Error-prone, slow, non-repeatable.
FROM node:18 WORKDIR /app COPY package*.json ./ RUN npm install COPY . . CMD ["node", "index.js"] Method 1: Inline in Compose file (bad for secrets) environment: - API_KEY=secret123 Method 2: .env file (recommended for dev) # .env DB_PASSWORD=devpass API_PORT=3000 environment: - DB_PASSWORD=$DB_PASSWORD Method 3: env_file (for larger sets) env_file: - ./config/common.env Never commit .env with production secrets. Use .env.example in version control. 7. Healthchecks, Dependencies & Startup Order depends_on alone does not wait for the database to be ready – only for container start. docker volume create
redis: image: redis:7-alpine