Docker Compose

Docker Compose runs multiple containers together. It is common for local development and small deployments.

services:
  app:
    build: .
    ports: ["3000:3000"]
    environment:
      DATABASE_URL: postgres://postgres:postgres@db:5432/app
  db:
    image: postgres:16
    volumes:
      - db_data:/var/lib/postgresql/data
volumes:
  db_data:

WARNING

Containers are disposable. Databases need volumes or managed storage, or data disappears when containers are removed.

Further Learning

“Docker Compose services volumes” — compose basics
“Postgres Docker volume” — persistent DB data
“Docker Compose production caveats” — limits and tradeoffs

Docker Compose

Most real apps need more than one thing running — your app and a database, for example. Docker Compose lets you describe several containers together in one file and start them all with one command.

Describing your whole setup

services:
  app:
    build: .
    ports: ["3000:3000"]
    environment:
      DATABASE_URL: postgres://postgres:postgres@db:5432/app
  db:
    image: postgres:16
    volumes:
      - db_data:/var/lib/postgresql/data
volumes:
  db_data:

One docker compose up and both your app and its database spin up together, already able to talk to each other (the app reaches the database just by using its service name, db, as the hostname).

Don’t lose your data

WARNING

Containers are disposable — if you remove a database container without a volume, all its data vanishes. The volumes: section above keeps the actual database files stored outside the container, so they survive even if the container is recreated.

Where it fits

Docker Compose is great for local development and small projects. For serious production deployments with lots of traffic, you’d typically graduate to something more robust (like Kubernetes or a managed hosting platform) — but Compose is the perfect way to get a multi-service app running locally in minutes.

In one sentence

Docker Compose describes multiple containers (like your app + its database) in one file so they start together — just remember to use volumes for anything you don’t want to lose when a container is removed.

Want to go deeper?

Switch to Expert mode above for production caveats and when to move beyond Compose.