Create a Scalable Web App with Docker Compose in Under 5 Minutes

Hey devs! If you've ever found yourself juggling multiple docker run commands or struggling to connect services together in development, Docker Compose is your new best friend.

In this post, I’ll walk you through:

• What Docker Compose is

• Why it's a game-changer

• A hands-on demo using Flask + Redis

• How to run it locally in 3 simple steps

Let’s dive in! 🐳

🧠 What is Docker Compose?

Docker Compose is a tool that allows you to define and run multi-container Docker applications using a YAML file.

Rather than starting each container individually with docker run, you define all services (like web apps, databases, and caches) in one file—then start everything with a single command:

docker-compose up

That’s it. Your entire app spins up.

💡 Perfect for:

• Web apps that use backend + database + cache

• Microservices

• Development and testing environments

🧠 Why Use Docker Compose?

✅ One command to run everything
✅ Simple service linking (like Flask talking to Redis or MySQL)
✅ Easier sharing and collaboration
✅ Reproducible environments

📦 Project Overview

We’ll create:

• A Flask app that shows how many times it has been visited

• A Redis cache that stores the count

🧱 Project Structure

myapp/
├── app.py
├── requirements.txt
├── Dockerfile
└── docker-compose.yml

🧾 Step 1: Flask App Code

Create a file named app.py:

from flask import Flask
import redis

app = Flask(__name__)
cache = redis.Redis(host='redis', port=6379)

@app.route('/')
def hello():
    count = cache.incr('hits')
    return f'Hello! You have visited this page {count} times.\n'

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000)

🔍 This does 3 things:

• Connects to Redis (host='redis')

• Increments a key hits

• Returns how many times the page is visited

📦 Step 2: Add Requirements

Create a file named requirements.txt:

flask
redis

🐋 Step 3: Create Dockerfile

FROM python:3.9-alpine

WORKDIR /app
COPY . .
RUN pip install -r requirements.txt

CMD ["python", "app.py"]

This builds your Flask app into a Docker container using a lightweight Python image.

⚙️ Step 4: Create docker-compose.yml

version: "3.9"
services:
  web:
    build: .
    ports:
      - "5000:5000"
    depends_on:
      - redis

  redis:
    image: "redis:alpine"

• web is your Flask app

• redis is a Redis cache pulled from Docker Hub

• depends_on ensures Redis starts before Flask tries to connect

🚀 Run the App

Step-by-step:

Open terminal and navigate to the project directory

cd myapp

Run Docker Compose

docker-compose up --build

Open in your browser:

http://localhost:5000

You’ll see:

Hello! You have visited this page 1 times.

Keep refreshing! Redis increments the counter.

🧪 Bonus: Tear Down the App

To stop and remove containers:

docker-compose down

To stop and delete containers, volumes, and networks:

docker-compose down -v

💡 What You Learned

✅ How Docker Compose links multiple services
✅ Creating and connecting a Flask app with Redis
✅ Dockerizing and running everything with a single command

🛠️ Ideas to Extend This Demo

• Add PostgreSQL or MySQL to store persistent data

• Use Docker Volumes to persist Redis across reboots

• Deploy the app on a cloud VPS using Docker Compose

📈 Want to Boost Your DevOps Skills?

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• More beginner-friendly Docker guides

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• Deployment, CI/CD, and cloud tutorials

💬 Got stuck somewhere? Drop your questions in the comments — I reply fast!

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