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Create a Compose File¶

When to Use This Guide¶

Use this guide to write a Compose file that describes a multi-container application in one place.

Quick Command

docker compose up -d

Step 1: Create the File¶

In your project folder, create a file named compose.yaml.

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

  app:
    build: .
    ports:
      - "8000:5000"
    environment:
      DB_HOST: db
    depends_on:
      - db

volumes:
  db-data:

Step 2: Understand the Parts¶

services: each container in your app
image or build: use a ready image, or build from a local Dockerfile
ports: publish a port to your host
environment: pass settings in
volumes (at the bottom): declare named volumes for lasting data

Services reach each other by their service name, so app connects to the database at the host db.

File Naming¶

The modern name is compose.yaml. The older docker-compose.yml still works, and Docker recognises both.

Common Issues¶

Indentation errors

YAML is strict about spaces. Use consistent two-space indentation, and never use tabs.