Docker Compose – Managing Multi-Container Apps

1. Introduction

Running a single Docker container is easy, but what if your app needs multiple services, like a web app + database? Managing multiple containers manually can be time-consuming.

🚀 Docker Compose solves this by allowing you to define and run multi-container applications with a single command.

In this guide, you’ll learn what Docker Compose is, how to write a docker-compose.yml file, and how to run multiple services efficiently.

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2. What is Docker Compose?

Docker Compose is a tool that allows you to:
✅ Define multiple containers in one file (docker-compose.yml)
✅ Start all containers with one command
✅ Easily manage and scale multi-container applications

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3. Why Use docker-compose.yml?

Instead of running multiple docker run commands, Compose lets you define all services in a single file.

Without Compose:

docker run -d --name db -e MYSQL_ROOT_PASSWORD=root mysql
docker run -d --name app --link db my-app

You have to manually start each container. 😓

With Compose (Simple & Clean!):

docker-compose up -d

🚀 Everything starts with one command!

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4. Writing a Basic docker-compose.yml File

Let’s define a web app + MySQL database using Compose.

Step 1: Create a docker-compose.yml File

version: '3.8'

services:
  db:
    image: mysql
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: root

  app:
    image: my-web-app
    depends_on:
      - db
    ports:
      - "8080:80"

✅ This file defines two services (app and db) that run together.

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5. Running Multiple Services with Compose

Step 1: Start All Containers

docker-compose up -d

✅ This starts the web app and database at the same time!

Step 2: Check Running Containers

docker-compose ps

Step 3: Stop All Services

docker-compose down

✅ This stops and removes all containers at once.

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6. Using Environment Variables in Compose

Instead of hardcoding passwords, store them in an environment file.

Step 1: Create a .env File

MYSQL_ROOT_PASSWORD=mysecretpassword

Step 2: Modify docker-compose.yml to Use It

version: '3.8'

services:
  db:
    image: mysql
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}

✅ This keeps your credentials secure & configurable.

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7. Conclusion

Docker Compose makes managing multi-container apps super easy! Now you can:
✅ Write a docker-compose.yml file
✅ Run multiple containers with one command
✅ Use environment variables for security

Start using Compose today to simplify your Docker workflow! 🚀