docker-compose.yml

Relax. We'll talk through this in plain words — no textbook voice.

docker-compose.yml is a YAML-format configuration file. It lets you write out the services, images, ports, volumes, and environment variables your app needs in a readable way.

dockerfile

# Create a file named docker-compose.yml
services:
  web:
    image: nginx:alpine
    ports:
      - "8080:80"
  redis:
    image: redis:alpine
    volumes:
      - redis-data:/data

volumes:
  redis-data:

web service runs Nginx and maps it to host port 8080. The redis service runs a Redis cache and stores its data in the redis-data volume.

You should see

This file defines a stack with two services: a web server and Redis.

Info

Docker creates a Compose network by default, so services can reach each other by service name. For example, from inside the web app, you can connect to Redis at redis:6379.

Easy traps

Don't use tabs in YAML — stick to space indentation. Small mistakes with colons, dashes, or quotes can easily trigger Compose errors.