URL Shortener

A URL shortener looks trivial: store a mapping from a short code to a long URL, and redirect on lookup. That is exactly why it is a favorite warm-up in FAANG interviews. The interesting engineering is not the data model, which is a single key-value row, but the traffic shape. Redirects outnumber creates by roughly 100 to 1, and the redirect path sits in the critical path of every shared link on the internet. A dead redirect path is a dead product, so the whole design problem is really about making reads cheap, fast, and resilient to the datastore going dark. This guide walks you to the reference architecture the SysGym simulator grades you against. The scenario starts at 4,000 redirects per second, ramps toward a 3x peak of 12,000 rps as a celebrity shares a link, drops the datastore as that surge hits, and then lets the store limp back with an 8x latency spike. Your job is to keep redirects succeeding at 99% availability with a sustained p99 at or below 110 ms while spending a lean footprint. We will derive every component and every number from first principles, then map them back to the exact SLOs and the reference graph so the article and the gym reinforce each other.