Design Dropbox

Dropbox is a file hosting and synchronization service. A user installs a client on multiple devices (laptop, phone, web), drops files into a magic folder, and those files appear on every other device within seconds. The same abstraction also supports sharing, version history, and collaboration.

What makes the problem interesting is the combination of huge blob payloads, tight sync latency, and multi-device consistency. You have to hold a durable petabyte-scale file store, a strongly consistent metadata database, and a low-latency push channel to every connected client, all at once.

This walkthrough follows the Interview Framework and is sized for a 45 to 60 minute interview.