docker-compose

docker-compose

Production-grade docker-compose.yml authoring for multi-service applications. Covers dependency graphs, conditional service activation, config layering, and zero-downtime update strategies.

Dependency Ordering with Health Checks

depends_on with condition: service_healthy prevents race conditions at startup. Without it, your app starts before the database is ready to accept connections.

services:
  api:
    build: .
    depends_on:
      db:
        condition: service_healthy
      redis:
        condition: service_healthy
      migrations:
        condition: service_completed_successfully   # one-shot jobs

  db:
    image: postgres:16
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U $$POSTGRES_USER"]
      interval: 5s
      timeout: 3s
      retries: 5

  redis:
    image: redis:7-alpine
    healthcheck:
      test: ["CMD", "redis-cli", "ping"]
      interval: 5s

  migrations:
    image: myapp:latest
    command: ["alembic", "upgrade", "head"]
    depends_on:
      db:
        condition: service_healthy
    restart: "no"   # one-shot — do not restart after completion

Compose Profiles (Selective Service Activation)

Profiles let you activate subsets of services without maintaining separate files.

services:
  api:
    build: .
    # no profile — always started

  worker:
    build: .
    command: celery -A app worker
    profiles: [worker]         # only started with --profile worker

  flower:
    image: mher/flower
    profiles: [worker, debug]  # started with either --profile worker or --profile debug

  mailhog:
    image: mailhog/mailhog
    profiles: [debug]          # local email testing only
    ports:
      - "127.0.0.1:8025:8025"

  adminer:
    image: adminer
    profiles: [debug]
    ports:
      - "127.0.0.1:8080:8080"

# Start only core services
docker compose up -d

# Start core + worker profile
docker compose --profile worker up -d

# Start everything for local debugging
docker compose --profile worker --profile debug up -d