Designing a URL Shortener

Designing a URL shortener is one of the most popular system design interview questions. It looks simple — but it tests your understanding of scalability, databases, caching, distributed systems, and trade-offs. Let’s break it down in a way that’s easy to understand and easy to remember. Step 1: Clarify Requirements Before jumping into architecture, always clarify requirements. Functional Requirements Users should be able to create a short URL from a long URL. When users visit the short URL, they should be redirected to the original URL. Optional: Custom alias (e.g., short.ly/myname) Expiry time for links Analytics (click count, geo, device info) Non-Functional Requirements High availability (service should almost never go down) Low latency redirection (redirect should feel instant) Massive scale (millions of URLs, billions of redirects) Durable storage (no data loss even if a server crashes) 👉 URL shorteners are read-heavy systems. Redirects happen far more often than URL creations. St