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.

The image shows a Visual Studio Code interface with a README.md file open, describing a Docker Flask application written in Python to be deployed on GKE. The file is displayed in both markdown and preview modes.

2. Project File Structure

File	Purpose
README.md	Overview and setup instructions
app.py	Flask application entrypoint
requirements.txt	Python dependencies
Dockerfile	Docker container build instructions

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

If Flask does not auto-detect app.py, you can set the environment variable:

ENV FLASK_APP=app.py

or change the CMD to:

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.

Introduction

Sprint-02

Sprint-03

Sprint-04

Sprint-05

Sprint-06

Sprint-07

Conclusion

Sprint-01

Task 4 Coding our application locally

Prerequisites

1. Update the README

2. Project File Structure

3. Create the Flask Application

4. Specify Dependencies

5. Write the Dockerfile

Next Steps

Links and References

Watch Video

​Prerequisites

​1. Update the README

​2. Project File Structure

​3. Create the Flask Application

​4. Specify Dependencies

​5. Write the Dockerfile

​Next Steps

​Links and References

Watch Video

Prerequisites

1. Update the README

2. Project File Structure

3. Create the Flask Application

4. Specify Dependencies

5. Write the Dockerfile

Next Steps

Links and References