# 🚀 I Built a Jenkins CI/CD Pipeline From Scratch — Here's Every Bug I Hit (and How I Fixed Them)

A learning-in-public story about Flask, Jenkins, AWS EC2, systemd, and finally shipping a live demo on Vercel. 🎯 TL;DR I built PyPulse, a tiny Flask app, and wired it up to a full CI/CD pipeline: push to GitHub → Jenkins builds → tests → deploys to AWS EC2 → auto-triggered via webhook → managed by systemd. Along the way I broke almost every piece of it at least once, and fixed each one. I also deployed a permanent live demo on Vercel, since my EC2 instance is running on the AWS free trial and won't live forever. 🔗 Live demo: pypulse-pi.vercel.app 🔗 Live demo (health check): pypulse-pi.vercel.app/health If you're learning DevOps and want to see what the real, messy version of "just set up a CI/CD pipeline" looks like — not the polished tutorial version — this is that. 🧰 The Stack Piece Tool Job App Flask + pytest + gunicorn The actual web app and its tests CI/CD Jenkins (on EC2, Ubuntu 22.04) Build → Test → Deploy automation Source control GitHub Single source of truth Trigger GitHub Webhook Auto-runs the pipeline on every push Process management systemd Keeps the app alive on reboot/crash Permanent demo Vercel Live URL that survives EC2 termination 🏗️ The App: PyPulse Nothing fancy on purpose — the whole point of this project was the pipeline, not the app. python app.py from flask import Flask, jsonify from datetime import datetime, timezone app = Flask( name ) @app.route("/") def home(): return jsonify({ "message": "Hello from PyPulse", "time": datetime.now(timezone.utc).isoformat() }) @app.route("/health") def health(): return jsonify({"status": "ok"}), 200 if name == " main ": app.run(host="0.0.0.0", port=5000) Two routes. Two tests. That's it. Small enough that when something broke, I knew it wasn't the app — it was the plumbing around it. That turned out to be the right call, because the plumbing broke a lot. 😅 ⚙️ The Pipeline: Build → Test → Deploy Here's the mental model I ended up with for a Jenkinsfile: Each stage is a gate. If Build fails, Test never runs.