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Design a URL Shortener (like bit.ly)

System DesignURL ShortenerDatabaseScalability

Question

How would you design a URL shortener service like bit.ly? Discuss the system architecture, database design, and scalability considerations.

Answer

System Requirements:

- Shorten long URLs

- Redirect short URLs to original URLs

- Handle high traffic (millions of requests per day)

- Short URLs should be unique and short (6-8 characters)

System Design:

1. API Design:

- POST /api/v1/shorten - Create short URL

- GET /{shortCode} - Redirect to original URL

2. Database Schema:

   ShortURLs:
   - id (primary key)
   - short_code (unique, indexed)
   - original_url (indexed)
   - created_at
   - expires_at (optional)
   - click_count

3. Encoding Algorithm:

- Base62 encoding (0-9, a-z, A-Z)

- Generate unique 6-8 character codes

- Use counter or hash-based approach

4. Caching:

- Use Redis to cache frequently accessed URLs

- Cache original_url by short_code

5. Scalability:

- Load balancers for traffic distribution

- Database sharding by short_code

- CDN for static assets

- Rate limiting to prevent abuse

Explanation

This is a classic system design problem that tests your understanding of: - Database design and indexing - Caching strategies - Scalability and performance optimization - API design - Distributed systems concepts