Python Hello World — Docker + Jenkins (Flask Web App)

A practical, hands-on example that demonstrates how to create a Python Flask web app, containerize it with Docker, and automate builds and publishing using Jenkins. This project is designed as a foundation for CI/CD experimentation, easily adaptable to your own projects.

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Why this repository exists

• Teach the basics of containerizing a Python app.
• Show a minimal Dockerfile and how to build/run images locally.
• Provide a sample Jenkins pipeline to automate image builds and pushes to Docker Hub.
• Serve as a starting point for CI/CD experiments.

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What you’ll find here

• helloworld.py — a simple Flask web app that responds in the browser
• Dockerfile — packages the Flask app into a minimal image
• Jenkinsfile — an optional Declarative Pipeline that builds and pushes the image

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Workflow Overview

Visual representation of the pipeline:

flowchart LR
    A["Python Flask App - helloworld.py"] --> B["Docker - Build & Containerize"]
    B --> C["Jenkins - Build & Push Pipeline"]
    C --> D["Docker Hub - Container Registry"]

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Project structure

.
├── Dockerfile
├── Jenkinsfile     # example pipeline (optional)
└── helloworld.py

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Getting started — local workflow

Replace assign-stone with your Docker Hub username if publishing under a different account.

1. Clone the repository

git clone https://github.com/assign-stone/python-hello-world-docker-jenkins.git
cd python-hello-world-docker-jenkins

2. Inspect or create the Flask app

# helloworld.py
from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello():
    return "Hello, World from Dockerized Flask App!"

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

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3. Create or review the Dockerfile

FROM python:3.12-slim

WORKDIR /app

# Install Flask
RUN pip install --no-cache-dir flask

COPY helloworld.py .

# Expose Flask port
EXPOSE 5000

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

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4. Run the container locally (EC2)

docker build -t assign-stone/pythonhelloworld:latest .
docker run -p 5000:5000 assign-stone/pythonhelloworld:latest

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5. Access the app in a browser via EC2 public IP

1. Go to EC2 Console → Your Instance → Security Groups → Inbound Rules
2. Add a rule to allow traffic on port 5000 from 0.0.0.0/0 (or your IP).
3. Open a browser and go to:

http://<EC2_PUBLIC_IP>:5000

You should see:

Hello, World from Dockerized Flask App!

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Publishing to Docker Hub

1. Log in:

docker login

2. Tag and push the image:

docker tag assign-stone/pythonhelloworld:latest assign-stone/pythonhelloworld:latest
docker push assign-stone/pythonhelloworld:latest

3. Pull and run from another host:

docker pull assign-stone/pythonhelloworld:latest
docker run -p 5000:5000 assign-stone/pythonhelloworld:latest

Then access in the browser:

http://<host-ip>:5000

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Jenkins CI — example pipeline

The Jenkinsfile demonstrates:

• Checking out the repo
• Building a Docker image and tagging it
• Pushing the image to Docker Hub using Jenkins credentials

Jenkinsfile example:

pipeline {
    agent any

    environment {
        DOCKERHUB_CREDENTIALS = credentials('dockerhub')
        IMAGE_NAME = "shivanijoshi38/pythonhelloworld"
    }

    stages {
        stage('Checkout Code') {
            steps {
                git branch: 'main', url: 'https://github.com/assign-stone/python-hello-world-docker-jenkins.git'
            }
        }

        stage('Build Docker Image') {
            steps {
                script {
                    sh "docker build -t ${IMAGE_NAME}:latest ."
                }
            }
        }

        stage('Push to Docker Hub') {
            steps {
                script {
                    withDockerRegistry([credentialsId: 'dockerhub', url: '']) {
                        sh "docker push ${IMAGE_NAME}:latest"
                    }
                }
            }
        }
    }
}

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Jenkins setup notes

• Create a Jenkins credential (dockerhub) containing your Docker Hub username and password.
• Ensure the Jenkins agent has Docker installed and can run Docker commands.
• For multi-branch pipelines, enable branch scanning to automatically build any branch containing a Jenkinsfile.

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Troubleshooting tips

• Docker build fails → Ensure Jenkins user has access to the Docker daemon.
• Docker push fails → Verify credentials and that the Jenkins credential ID matches.
• Cannot access Flask app via EC2 → Check security group inbound rules and use host="0.0.0.0" in Flask app.

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Contributing

We love contributions! 🚀

Whether it’s improving the CI/CD workflow, adding tests, enhancing documentation, implementing secure Docker practices, or sharing new ideas, your help makes this project better for everyone. Open an issue, submit a pull request, or suggest improvements — all contributions are welcome!

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License

MIT License — feel free to reuse and adapt.

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Author

• assign-stone