Design a Scalable URL Shortening Platform

Context

Build a Bitly-like URL shortener that maps long URLs to short codes and performs HTTP redirection reliably at global scale. Assume the service is read-heavy, stores billions of links, and must meet low latency and high availability requirements.

Requirements

1. APIs

• Define REST APIs for:
  • Create short link (with optional custom alias and TTL)
  • Expand short code to original URL (preview)
  • Delete/disable a short link

2. Short Code Generation

• Strategy: hashing and/or counter-based IDs
• Base-N encoding (e.g., base62)
• Collision handling
• Support custom aliases
• TTL/expiration behavior

3. Data Model and Storage

• Schema for links, users, and analytics
• Storage for billions of links (trade-offs: SQL vs NoSQL, KV stores)
• Indexing and sharding strategy

4. Read-Heavy Architecture

• Caches (edge and regional)
• CDN and edge compute considerations
• Redirect behavior (301/302/307) and caching semantics

5. Rate Limiting and Abuse Prevention

• Per-IP/account rate limiting
• Malware/phishing detection, Safe Browsing integration
• Blacklist/allowlist, link scanning

6. Analytics

• Click counts, uniques, geo, time-of-day
• Real-time vs batch pipelines

7. GDPR/Compliance

• Data minimization, retention, encryption
• Right-to-be-forgotten, data residency

8. Capacity Plan

• QPS estimates (create vs redirect)
• Storage sizing (links and logs)

9. Fault-Tolerant Deployment

• Multi-AZ/region replication
• Sharding, failover

10. Consistency Trade-offs

• Strong vs eventual consistency (creation, expansion, deletion)
• Global uniqueness of custom aliases