Building CI/CD Pipelines for Flask Applications

Introduction

Continuous Integration and Continuous Deployment (CI/CD) play a crucial role in modern software development. Automating the testing, building, and deployment process ensures faster delivery, fewer errors, and improved reliability.

In this guide, we will explore how to build a CI/CD pipeline for Flask applications using:

✅ GitHub Actions for automated builds and testing
✅ Docker for containerization
✅ Kubernetes for deployment
✅ NGINX/Gunicorn for production-ready hosting

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Setting Up Flask for CI/CD

Before setting up the pipeline, ensure your Flask project has:

• A GitHub repository
• A requirements.txt file for dependencies
• A Dockerfile for containerization
• A test suite using pytest

Step 1: Create a Basic Flask Application

from flask import Flask

app = Flask(__name__)

@app.route("/")
def home():
return "Hello, CI/CD Pipeline!"

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

Step 2: Add Dependencies

Create a requirements.txt file:

Flask
pytest

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Writing Unit Tests

Automated testing is crucial in CI/CD pipelines. Let’s write a simple pytest test case.

Create a test_app.py file:

import pytest
from app import app

@pytest.fixture
def client():
app.testing = True
return app.test_client()

def test_home(client):
response = client.get("/")
assert response.status_code == 200
assert b"Hello, CI/CD Pipeline!" in response.data

Run tests locally:

pytest

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Dockerizing the Flask Application

Step 3: Create a Dockerfile

# Use official Python image
FROM python:3.9

# Set the working directory
WORKDIR /app

# Copy application files
COPY . /app

# Install dependencies
RUN pip install -r requirements.txt

# Expose port 5000
EXPOSE 5000

# Start Flask application
CMD ["python", "app.py"]

Build and run the Docker container:

docker build -t flask-ci-cd .
docker run -p 5000:5000 flask-ci-cd

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Setting Up GitHub Actions for CI

GitHub Actions automates testing and deployment.

Step 4: Create a .github/workflows/ci.yml File

name: Flask CI Pipeline

on:
push:
branches:
- main
pull_request:
branches:
- main

jobs:
test:
runs-on: ubuntu-latest
steps:
- name: Checkout Code
uses: actions/checkout@v3

      - name: Set Up Python
        uses: actions/setup-python@v3
        with:
          python-version: "3.9"

      - name: Install Dependencies
        run: |
          pip install -r requirements.txt

      - name: Run Tests
        run: pytest

This workflow automatically runs tests on every push or pull request.

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Deploying with Docker and Kubernetes

Step 5: Create a Kubernetes Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
name: flask-app
spec:
replicas: 2
selector:
matchLabels:
app: flask
template:
metadata:
labels:
app: flask
spec:
containers:
- name: flask-container
image: your-dockerhub-username/flask-ci-cd:latest
ports:
- containerPort: 5000

Apply the deployment:

kubectl apply -f deployment.yml

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Automating Deployment with GitHub Actions

Step 6: Extend GitHub Actions for Deployment

Modify .github/workflows/ci.yml to include Docker build & push:

build-and-deploy:
needs: test
runs-on: ubuntu-latest
steps:
- name: Checkout Code
uses: actions/checkout@v3

      - name: Set Up Docker
        run: |
          echo "$" | docker login -u "$" --password-stdin
          docker build -t your-dockerhub-username/flask-ci-cd .
          docker tag your-dockerhub-username/flask-ci-cd your-dockerhub-username/flask-ci-cd:latest
          docker push your-dockerhub-username/flask-ci-cd:latest

Step 7: Deploy to Kubernetes

- name: Deploy to Kubernetes
run: |
echo "$" | base64 --decode > kubeconfig
kubectl --kubeconfig=kubeconfig apply -f deployment.yml

This ensures automatic deployment to Kubernetes after successful tests.

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Conclusion

🚀 Key Takeaways:

✅ Automated Testing using GitHub Actions
✅ Containerization with Docker
✅ Automated Deployments with Kubernetes

By implementing CI/CD, you can ensure smooth, reliable, and automated deployments of your Flask applications.

🔗 Next Steps: Integrate with Helm Charts, set up CDNs, or explore serverless deployments!

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