🐳 Building a Simple "Hello World" Docker Project

🚀 This is my the first project I have ever done using Docker. I did this to teach myself the basics of Containerization.

In this guide, we'll create a containerized Python web application that displays a "Hello World" message. This tutorial works on Ubuntu/Debian-based Linux distributions

🔹 System Preparation

Before we start, update and upgrade your system packages:

bash

sudo apt update
sudo apt upgrade -y

Install Docker and other required dependencies:

bash

sudo apt install ca-certificates curl gnupg

Add Docker’s Official GPG Key

bash

sudo install -m 0755 -d /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo tee /etc/apt/keyrings/docker.asc > /dev/null
sudo chmod a+r /etc/apt/keyrings/docker.asc

Add Docker Repository

bash

echo "deb [signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Install Docker

bash

sudo apt update
sudo apt install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Verify Installation

Check if Docker is installed:

bash

docker --version

Start and enable Docker:

bash

sudo systemctl enable --now docker

Check Docker status:

bash

sudo systemctl status docker

🔹 Install Docker Compose Plugin

Ubuntu now uses the Docker Compose plugin instead of the standalone binary:

bash

sudo apt install docker-compose-plugin -y

Verify installation:

bash

docker compose version

Install Python Pip for dependencies:

bash

sudo apt install python3-pip
python3 -m pip install --upgrade pip

🔹 Create Project Directory

Set up the directory structure:

bash

mkdir docker-projects
cd docker-projects

🔹 Create Python Web Application

Create the app.py file:

bash

touch app.py
nano app.py

Copy & paste the following Python Flask app:

python

from flask import Flask
import redis

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

def get_hit_count():
    try:
        return cache.incr('hits')
    except redis.exceptions.ConnectionError:
        return 1

@app.route('/')
def hello():
    count = get_hit_count()
    return f"Hello World! You have visited {count} times."

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

Save the file (CTRL + X, then Y).

🔹 Define Dependencies

Create the requirements.txt file:

bash

touch requirements.txt
nano requirements.txt

Add dependencies inside requirements.txt file:

Flask
redis

Save (CTRL + X, then Y).

🔹 Create Dockerfile

Create a Dockerfile:

bash

touch Dockerfile
nano Dockerfile

Paste the following Dockerfile configuration:

dockerfile

FROM python:3.9

WORKDIR /app
COPY . .
RUN pip install -r requirements.txt
CMD ["python", "app.py"]

Save (CTRL + X, then Y).

🔹 Configure Docker Compose

Create the docker-compose.yml file:

bash

touch docker-compose.yml
nano docker-compose.yml

Paste the Docker Compose config:

yaml

version: '3'

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

  redis:
    image: "redis:alpine"

Save (CTRL + X, then Y). ⚠ YAML files are sensitive to indentation—validate them before running!

🔹 Build and Run the Project

Ensure you're in the docker-projects directory:

bash

cd docker-projects

Start the containers:

bash

sudo docker-compose up --build

🔹 Test the Web App

• Open a browser and go to http://localhost:5000

• You should see:

    Hello World! You have visited 1 times.
  

• Refreshing the page will increase the visitor count.

🔹 Stop Containers

Shut down the containers when you're done:

bash

sudo docker-compose down