Task 4 Coding our application locally

Welcome back! In this task, we’ll set up and test our Flask application on your local machine before pushing it to our GitHub repository. We’ll use VS Code for development, write the application code, declare dependencies, and containerize with Docker.

Prerequisites

• VS Code: https://code.visualstudio.com
• Python 3.8+
• Docker installed locally
• Git configured for your project

1. Update the README

Open README.md in VS Code and add a clear project title and description:

A simple Python Flask application containerized with Docker.  
This app will later be deployed on Google Kubernetes Engine (GKE).

Use VS Code’s Markdown Preview (⌘+Shift+V / Ctrl+Shift+V) to verify formatting.

2. Project File Structure

3. Create the Flask Application

Create app.py at the project root with the following code:

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, Simple Flask application'

This defines a basic web server with one route (/) that returns a greeting.

4. Specify Dependencies

In requirements.txt, list your Python packages:

Flask

This tells pip which libraries to install inside the container.

5. Write the Dockerfile

Create Dockerfile and add:

FROM python:3.8-slim-buster

WORKDIR /app

COPY requirements.txt requirements.txt
RUN pip3 install --no-cache-dir -r requirements.txt

COPY . .

CMD ["python3", "-m", "flask", "run", "--host=0.0.0.0"]

Key steps:

• Use a lightweight Python base image
• Copy and install dependencies
• Copy application code
• Expose Flask on all network interfaces

ENV FLASK_APP=app.py

CMD ["python3", "app.py"]

Next Steps

With your files in place (README.md, app.py, requirements.txt, Dockerfile), you’re ready to build and run the Docker image locally:

docker build -t flask-app:local .
docker run -p 5000:5000 flask-app:local

Visit http://localhost:5000 to verify the “Hello, Simple Flask application” message.

Links and References

• Flask Documentation
• Docker Documentation
• Google Kubernetes Engine (GKE)