Docker Foundations·Ship the environment with the app

Compose a real stack

Compose describes services, networks and volumes in one reproducible file.

Beginner 14 min read Lesson 9 of 300 Challenge included

What you will be able to do

Keep secrets out of compose.yaml; use environment files or a secret manager.
Add healthchecks and depend_on with condition: service_healthy.
Use a distinct override file for local-only development settings.

In plain English

A Compose file is a local development contract. Service names become DNS names; depends_on controls start order but not readiness. Use healthchecks and wait for dependencies instead of sleeping.

compose.yamlYAML

services:
  app:
    build: .
    ports: ["3000:3000"]
    environment:
      DATABASE_URL: postgres://app:secret@db:5432/app
    depends_on:
      db:
        condition: service_healthy
  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_USER: app
      POSTGRES_PASSWORD: secret
      POSTGRES_DB: app
    volumes:
      - pgdata:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U app"]
      interval: 5s
      retries: 10
volumes:
  pgdata:

Your turn

Add a healthcheck

Medium

Add a pg_isready healthcheck to a Postgres service and make the app depend on it being healthy.

YAML · starter

services:
  app:
    image: my-app

Check your understanding before moving on.

Knowledge checkQuestion 1

What does depends_on with service_healthy wait for?

Select an answer to continue

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