Docker Compose — Profiles & Extensions — Practice Exercises

1 minute read

Test your understanding of profiles, extensions, anchors, and includes.

Exercise 1: Basic Profile

Add a debug profile to an adminer service so it only starts when explicitly requested.

Solution 
services:
  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: secret

  adminer:
    image: adminer
    ports:
      - "8080:8080"
    profiles:
      - debug

docker compose up -d                    # Only db starts
docker compose --profile debug up -d    # db + adminer start

Exercise 2: Multiple Profiles

Create three profiles: dev, test, monitoring. Assign services to appropriate profiles.

Solution 
services:
  api:
    image: myapi:latest

  mailhog:
    image: mailhog/mailhog
    profiles: [dev]

  test-runner:
    image: myapi:latest
    command: npm test
    profiles: [test]

  prometheus:
    image: prom/prometheus
    profiles: [monitoring]

docker compose --profile dev up -d
docker compose --profile test run --rm test-runner
docker compose --profile monitoring up -d

Exercise 3: YAML Extension

Extract common logging config into an x-logging extension and apply it to three services.

Solution 
x-logging: &logging
  logging:
    driver: json-file
    options:
      max-size: "10m"
      max-file: "3"

services:
  api:
    <<: *logging
    image: myapi:latest
  worker:
    <<: *logging
    image: myworker:latest
  scheduler:
    <<: *logging
    image: myscheduler:latest

Verify: docker compose config

Exercise 4: Anchors for Environment

Use a YAML anchor to share environment variables across services, then override one variable.

Solution 
x-env: &base-env
  LOG_LEVEL: info
  NODE_ENV: production

services:
  api:
    image: node:20-alpine
    environment:
      <<: *base-env
      PORT: "3000"

  worker:
    image: node:20-alpine
    environment:
      <<: *base-env
      LOG_LEVEL: debug    # Override base value

Exercise 5: Compose Include

Split a compose file into a main file and a separate database file using include:.

Solution

compose.yml:

include:
  - compose.db.yml

services:
  api:
    image: myapi:latest
    depends_on:
      - db

compose.db.yml:

services:
  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: secret
    volumes:
      - db-data:/var/lib/postgresql/data

volumes:
  db-data:

docker compose config    # Shows merged result
docker compose up -d     # Starts api + db

You may also enjoy