bit.ly system design — building a url shortener

every system design conversation eventually circles back to bit.ly. it's the canonical "looks dead simple but isn't" service — take a long url, hand back a short one, redirect on click. the surface is straightforward. then you start asking how it scales to a billion urls and 100M daily active users, and the design gets way more interesting. this is a full walkthrough — requirements, api, the…