URLDN — System Design: URL Shortener

A modern system design case study for building a scalable URL shortening service like Bitly or TinyURL.

This project focuses on designing a high-performance distributed system capable of handling millions of redirects, analytics events, and URL generations at scale.

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Overview

URLDN demonstrates the architecture and engineering decisions behind a production-grade URL shortener.

The system supports:

• URL shortening
• Fast redirection
• Analytics tracking
• Distributed scalability
• High availability
• Caching strategies
• Database scaling

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Problem Statement

Design a URL shortening service that:

• Converts long URLs into short links
• Redirects users efficiently
• Handles massive traffic
• Supports analytics
• Maintains high availability

Example:

Input:
https://www.example.com/blog/how-to-build-distributed-systems

Output:
https://urldn.com/AbX91qK

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Functional Requirements

URL Shortening

Generate short URLs from long URLs.

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URL Redirecting

Redirect users instantly to the original URL.

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Analytics

Track:

• Click count
• Country
• Device
• Browser
• Referrer
• Timestamp

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Custom Aliases

Example:

https://urldn.com/github

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Non-Functional Requirements

• High scalability
• High availability
• Fault tolerance
• Low latency redirects
• Horizontal scaling
• Reliability

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Traffic Estimation

Write Traffic

100 million URLs/day
≈ 1157 writes/sec

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Read Traffic

Assuming read/write ratio = 10:1

≈ 11,570 reads/sec

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High-Level Architecture

Clients
   ↓
CDN / Cloudflare
   ↓
Load Balancer
   ↓
API Servers
   ↓
Redis Cache
   ↓
PostgreSQL
   ↓
Analytics Queue
   ↓
ClickHouse

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API Design

Create Short URL

POST /api/v1/urls

Request:

{
  "longUrl": "https://github.com/lahcenassmira"
}

Response:

{
  "shortUrl": "https://urldn.com/AbX91qK"
}

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Redirect URL

GET /:shortCode

Response:

301 Redirect
Location: https://github.com/lahcenassmira

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URL Redirect Flow

Client Request
      ↓
Load Balancer
      ↓
Redis Cache Lookup
      ↓
Database Fallback
      ↓
301 / 302 Redirect

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Database Design

URL Table

Column	Type
id	BIGINT
short_code	VARCHAR
long_url	TEXT
created_at	TIMESTAMP

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Analytics Table

Column	Type
id	BIGINT
short_code	VARCHAR
country	VARCHAR
browser	VARCHAR
clicked_at	TIMESTAMP

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Hash Generation

Base62 Encoding

Characters used:

0-9
a-z
A-Z

Total:

62 characters

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Base62 Example

ID: 12581231
↓
Base62: 4Fz91
↓
https://urldn.com/4Fz91

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URL Creation Flow

1. User submits URL
2. Validate URL
3. Generate unique ID
4. Convert ID → Base62
5. Store in database
6. Cache in Redis
7. Return short URL

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Caching Strategy

Redis stores:

shortCode → longURL

Example:

AbX91qK → https://github.com/lahcenassmira

Benefits:

• Faster redirects
• Reduced database load
• Improved latency

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Scaling Strategy

Stateless API Servers

Easy horizontal scaling behind load balancers.

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Database Replication

Use read replicas for scaling reads.

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Queue-Based Analytics

Process analytics asynchronously to keep redirects fast.

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Security Considerations

• Rate limiting
• Spam protection
• DDoS mitigation
• URL validation
• Bot detection

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Tech Stack

Layer	Technology
Backend	Node.js + Express
Database	PostgreSQL
Cache	Redis
Analytics	ClickHouse
Queue	Kafka / RabbitMQ
Infrastructure	Docker
CDN	Cloudflare

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Future Improvements

• Smart redirects
• Geo-routing
• AI analytics
• QR code generation
• Edge redirects
• Link expiration
• Custom domains

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Conclusion

URLDN demonstrates the design of a scalable distributed URL shortener capable of handling millions of requests efficiently.

This project explores:

• Distributed systems
• Database scaling
• Caching
• System reliability
• API design
• High-performance architectures

Built for educational and system design learning purposes.