Design a Payment System

Each one worked end to end: requirements, estimates, the first diagram, the bottleneck that appears at scale, and the two or three deep dives an interviewer will push you into.

This module is 07.6 of the 6 in Design Case Studies. It runs about 4 hours across 5 lessons, and closes with Ledger — Process payments through a processor that times out, duplicates and lies. The ledger must still balance.