Episode 16: Docker Compose — Multi-Container Applications

#docker #devops #tutorial #container

In the previous episode, we explored Docker Networking and how containers communicate with each other. But as applications grow, managing multiple containers with just docker run becomes painful. This is where Docker Compose comes to the rescue.

🔹 What is Docker Compose?

Docker Compose is a tool that allows you to define and run multi-container Docker applications. Instead of starting each container manually, you define services in a single YAML file (docker-compose.yml) and bring everything up with one command.

🔹 Why Use Docker Compose?

Manage multiple containers easily.
Define networks and volumes in one place.
Consistent environment setup across teams.
One command (docker-compose up) starts the entire stack.

🔹 Installing Docker Compose

Most modern Docker installations already include Compose. To check:

docker compose version

If not installed, follow Docker’s official installation guide.

🔹 Basic `docker-compose.yml` Example

Let’s run a simple web app with Flask (Python) and Redis.

version: '3'
services:
  web:
    build: ./app
    ports:
      - "5000:5000"
    depends_on:
      - redis

  redis:
    image: redis:alpine

Here:

web → our Flask app (built from ./app directory).
redis → a Redis container using the official image.
depends_on → ensures redis starts before web.

🔹 Running the App

docker compose up

This will start both containers together.

To stop:

docker compose down

🔹 Adding Volumes & Networks

You can define persistent storage and custom networks:

version: '3'
services:
  db:
    image: postgres:alpine
    volumes:
      - db_data:/var/lib/postgresql/data

volumes:
  db_data:

This ensures your database data isn’t lost when the container restarts.

🔹 Real-World Example

A full-stack app might have:

Frontend (React/Next.js)
Backend (Node.js, Django, Flask, etc.)
Database (Postgres, MongoDB, MySQL)
Cache (Redis)

All defined in a single docker-compose.yml file.

🔹 Key Commands

docker compose up -d → start in detached mode.
docker compose down → stop and remove containers.
docker compose logs -f → view logs.
docker compose ps → list running services.

🔹 Best Practices

Use environment files (.env) to manage secrets.
Keep services modular (separate DB, cache, etc.).
Use volumes for persistent data.
Avoid hardcoding credentials inside docker-compose.yml.

✅ In the next episode, we’ll cover Episode 17: Docker Volumes & Persistent Data Management — making sure your data survives container restarts.

💡 Question for you: Do you want me to create a real-world multi-service app with Docker Compose (e.g., Node.js + MongoDB + Redis) in the upcoming episode?