Docker Compose Files and YAML Patterns

services:
  web:
    image: nginx:alpine
    ports:
      - "8080:80"
  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: secret

# Simple two-service stack with port publishing and environment variables.

services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
    image: myapp:dev

# Build a service image from local source while also tagging it.

services:
  worker:
    image: myapp:latest
    command: ["python", "worker.py"]

# Runs a different default command than the image CMD.

services:
  app:
    image: myapp:latest
    entrypoint: ["./docker-entrypoint.sh"]

# Overrides the image entrypoint.

services:
  redis:
    image: redis:7
    container_name: local-redis

# Pins a specific container name.

services:
  api:
    image: myapi:latest
    environment:
      NODE_ENV: development
      PORT: "3000"

# Provide container environment values inline in YAML.

services:
  api:
    image: myapi:latest
    environment:
      - NODE_ENV=development
      - PORT=3000

# Alternative environment syntax using `KEY=value` entries.

services:
  api:
    image: myapi:latest
    env_file:
      - .env
      - .env.local

# Loads container environment variables from one or more files.

services:
  api:
    image: "myapi:${APP_TAG:-latest}"
    ports:
      - "${APP_PORT:-3000}:3000"

# Uses shell-style variable interpolation inside the Compose file.

docker compose --env-file .env.production up -d

# Uses a specific env file when rendering the Compose project.

services:
  app:
    image: myapp:latest
  mailhog:
    image: mailhog/mailhog
    profiles: ["dev-tools"]

# Marks a service as optional unless its profile is enabled.

docker compose --profile dev-tools up -d

# Starts the stack with a selected optional profile enabled.

docker compose -f compose.yaml -f compose.override.yaml up -d

# Merges multiple Compose files in order.

docker compose -f compose.yaml -f compose.prod.yaml up -d

# Applies production overrides like replicas, image tags, and secrets.

services:
  web:
    image: myapp:latest
    depends_on:
      - db
  db:
    image: postgres:16

# Starts `db` before `web` in dependency order.

services:
  db:
    image: postgres:16
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 10s
      timeout: 5s
      retries: 5

# Defines a readiness-style health check for the service.

services:
  web:
    image: myapp:latest
    depends_on:
      db:
        condition: service_healthy
  db:
    image: postgres:16
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 10s
      timeout: 5s
      retries: 5

# Uses health state as the dependency condition for startup ordering.