Docker Compose Basics: Script Your First Multi-Container App

September 18, 2022

If you’ve ever run multiple services (like a database + a web server), you know how messy it gets to start each container manually. That’s where Docker Compose comes in. With one simple YAML file, you can define and run multi-container apps in seconds.

In this guide, you’ll learn the basics of Docker Compose by creating a simple PHP + MySQL app.

🐳 Step 1: Install Docker & Docker Compose

Make sure Docker is installed:

docker -v
docker compose version

If you see versions, you’re good to go.

⚡ Step 2: Create Your Project Files

We’ll make a folder with two files:

mkdir myapp && cd myapp
touch docker-compose.yml index.php

index.php (just a test page):

<?php
$host = "db";
$user = "root";
$pass = "example";
$dbname = "testdb";

$conn = new mysqli($host, $user, $pass, $dbname);

if($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

echo "Connected to MySQL successfully!";
?>

⚙️ Step 3: Docker Compose Script

Create docker-compose.yml:

version: "3.8"
services:
    web:
        image: php:8.2-apache
        volumes:
            - ./index.php:/var/www/html/index.php
        ports:
            - "8080:80"
        depends_on:
            - db

    db:
        image: mysql:8.0
        environment:
            MYSQL_ROOT_PASSWORD: example
            MYSQL_DATABASE: testdb
        volumes:
            - db_data:/var/lib/mysql

    volumes:
        db_data:

🚀 Step 4: Run It

Start your app with:

docker compose up -d

Open http://localhost:8080 you should see Connected to MySQL successfully!.

🎯 Why This Matters

• One command to start multiple containers
• Easy to scale and manage apps
• Standard for modern development

✅ You just learned Docker Compose basics and built your first multi-container app. Try extending it with phpMyAdmin or a Redis cache next!