InstructionsUbuntu.md

🐳 Building a Simple "Hello World" Docker Project

🚀 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 distros

---

🔹 System Preparation

Before we start, update and upgrade your system packages:

sudo apt update
sudo apt upgrade -y

Install Docker and other required dependencies:

sudo apt install ca-certificates curl gnupg

Add Docker’s Official GPG Key

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

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

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

Verify installation:

docker --version

Start and enable Docker:

sudo systemctl enable --now docker

Check Docker status:

sudo systemctl status docker

---

🔹 Install Docker Compose Plugin

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

sudo apt install docker-compose-plugin -y

Verify installation:

docker compose version

Install Python Pip for dependencies:

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

---

🔹 Create Project Directory

Set up the directory structure:

mkdir docker-projects
cd docker-projects

---

🔹 Create Python Web Application

Create the app.py file:

touch app.py
nano app.py

Copy & paste the following Python Flask app:

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:

touch requirements.txt
nano requirements.txt

Add dependencies inside requirements.txt:

Flask
redis

Save (CTRL + X, then Y).

---

🔹 Create Dockerfile

Create a Dockerfile:

touch Dockerfile
nano Dockerfile

Paste the following Dockerfile configuration:

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:

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

Paste the Docker Compose config:

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:

cd docker-projects

Start the containers:

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:

sudo docker-compose down