Compose design

Design the structure of a docker-compose.yml file.

Project: a multi-service app with Compose

Real applications don't consist of a single container: a web app, a database, maybe a cache. Starting each with long docker run commands is tedious and error-prone. Docker Compose defines all the services in a single compose.yaml file and manages them with one command:

docker compose up -d      # create and start all services
docker compose ps         # show their status
docker compose down       # stop and remove

In this project you'll build a Python API + PostgreSQL + Redis stack step by step.

The skeleton of compose.yaml

The file's top-level keys are services (containers), volumes (named volumes) and networks (custom networks). In YAML, indentation carries meaning; spaces are used, not tabs:

services:
  web:
    image: nginx:alpine
    ports:
      - "8080:80"

Instead of the old docker-compose (hyphenated, v1), the docker compose (v2) built into Docker is used now; the version: line at the top isn't needed either.

Exercise The first compose file

Write a compose.yaml: the web service uses the nginx:alpine image and maps host port 8080 to container port 80.

Show example solution

# compose.yaml
services:
  web:
    image: nginx:alpine
    ports:
      - "8080:80"

Test yourself

What is Compose's main advantage over docker run commands?
- Not needing images
- Working only in production
- All service settings live in one file under version control
- Faster containers
Show answer

All service settings live in one file under version control — Anyone who gets the file sets up the same stack with docker compose up.

Write the top-level key defining the services.

____:
  web:
    image: nginx:alpine

Show answer

services:
  web:
    image: nginx:alpine

Match.

services

Container definitions
volumes

Named volumes
docker compose up -d

Start the stack
docker compose down

Remove the stack

Next lesson: Service definition

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