How would you design a URL shortener like bit.ly?

🏗️ System Design• 9/21/2025
System design for URL shortening service covering encoding algorithms, database design, caching, and scalability considerations.

URL Shortener System Design

Requirements

Functional:

  • Shorten long URLs to short URLs
  • Redirect short URLs to original URLs
  • Custom aliases (optional)
  • URL expiration
  • Analytics

Non-Functional:

  • 100:1 read/write ratio
  • 100M URLs shortened per day
  • Low latency < 100ms
  • 99.9% availability

High-Level Architecture

[Client] → [Load Balancer] → [API Gateway] → [App Servers]
                                              ↓
[Cache Layer] ← → [Database] ← → [Analytics DB]

URL Encoding Approaches

  1. Base62 Encoding - Convert unique ID to base62
  2. Hash-based - MD5/SHA1 hash of URL
  3. Counter-based - Auto-incrementing counter

Database Design

  • Primary table: urls (id, short_url, long_url, created_at, expires_at)
  • Indexes on short_url for fast lookups
  • Sharding by short_url for scalability
By: System Admin