🔗 Scalable URL Shortener Microservice

A production-ready, distributed URL shortener platform built using Spring Boot Microservices, leveraging OAuth2, Kafka, Redis, MongoDB TTL, and JWT Authentication. This platform not only shortens links, but also supports ad-based interstitial redirection, rate limiting, and high scalability out of the box.

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📌 Project Highlights

• ✅ Unique short URL generation
• 🔐 OAuth2 & JWT-based Authentication
• ⚡ Redis caching for high performance
• 🧪 Token-secured API Gateway with Rate Limiting
• 📩 Kafka-based Event-Driven architecture
• ⏳ MongoDB TTL auto-expiry for short URLs
• 🧠 Bcrypt password encryption with MySQL User Service
• 🎯 10-second Interstitial Ad Page before redirect
• 📈 Modular, Multi-Repo, Dockerized Microservices

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🧱 System Architecture (C4 Architecture)

🌐 Flow Summary

1. User Login via /auth/login → receives JWT
2. Create Short URL via /shorten → saves in MongoDB, sends Kafka message
3. Caching Service listens to Kafka → caches URL in Redis with TTL
4. Redirect Request checks Redis → fallback to MongoDB → shows Ad page → redirects to original URL

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🔧 Technologies Used

Layer	Technology
Language	Java 17
Framework	Spring Boot 3.2, Spring WebFlux, Spring Security
Messaging	Apache Kafka
Database	MongoDB (TTL), MySQL
Caching	Redis
Auth	OAuth2, JWT, Bcrypt
Gateway	Spring Cloud Gateway
Monitoring	Spring Actuator
Frontend	Thymeleaf, JavaScript
DevOps	Docker, Docker Compose
Others	Lombok, SLF4J, Maven, Rate Limiting

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🚀 Getting Started

📥 Clone & Run (Dockerized)

git clone https://github.com/your-username/url-shortener.git
cd url-shortener
docker-compose up --build

🔐 Obtain JWT Token

curl --location 'http://localhost:8080/auth/login' --header 'Content-Type: application/json' --data '{
  "username": "testuser",
  "password": "123"
}'

🔗 Create Short URL

curl --location 'http://localhost:8080/shorten' --header 'Content-Type: application/json' --header 'Authorization: Bearer <your_jwt_token>' --data '{
  "longUrl": "https://google.com"
}'

🔁 Redirect Flow

http://localhost:8080/r/abc123 → redirects to ad page for 10s → redirects to original link

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📦 Data Persistence

Storage	Usage
MongoDB	Stores short URL mappings (TTL Index for expiry)
Redis	Caches hot URLs for fast resolution
MySQL	Stores user credentials securely (hashed with Bcrypt)

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📣 Interstitial Redirect Page

• Users are shown an ad/interstitial page for 10 seconds after accessing the short link
• Ads can be static banners, dynamic content, or affiliate promotions
• This feature is key to potential monetization strategy

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📚 Photo of Redirect Page and 404 page

🧪 Testing

./mvnw test

All critical modules are covered with unit tests, including edge cases and failure scenarios.

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🛡️ Security Considerations

• OAuth2 + JWT for authenticated APIs
• Rate Limiting at API Gateway (per IP / token)
• Sanitization of long URLs
• Password encryption using Bcrypt
• Secure Kafka communication (if TLS configured)

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🔁 Kafka Events

Topic	Description
create-url	Emitted when a short URL is created
url-visited	[Future] For tracking analytics

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📈 Monitoring & Health

• Exposed via /actuator endpoints
• Health, metrics, and readiness probes
• Can be integrated with Prometheus/Grafana

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📄 API Reference

Endpoint	Method	Auth	Description
/auth/login	POST	❌	Login and get JWT
/shorten	POST	✅	Create short URL
/r/{shortId}	GET	❌	Redirect to original URL

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📦 Versioning

We follow Semantic Versioning:

Current Version: 1.2.0

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📍 Contact

Feel free to reach out:

• Email: parsa10007@gmail.com
• GitHub Issues for bugs & feature requests

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Made with ☕, Spring, and ❤️ by [Parsa Eftekharmanesh]