Code It: Avoid Double Payments with Idempotency Keys (Python) | Payment System Design, Part 4

Code It: Exactly Once — part 4 of the Payment System Design build. A full system design walkthrough, drawn on the board as it is argued. Every diagram is built in front of you and every decision is defended out loud, the way it has to be in the room. 0:00 Twenty clicks, one charge 0:56 Code it: the state machine as a table 2:44 Code it: the atomic claim and the lease 4:23 Code it: confirm, look up and resolve 6:15 Code it: four planted bugs, caught 8:08 What the tests proved Playlist: Payment System Design — the complete build, in order. Part of a system design interview preparation series: full high-level design (HLD) walkthroughs for software engineering interviews, covering scalability, distributed systems, capacity estimation and the trade-offs an interviewer will push on. Every build is complete or releasing now; more in production. #systemdesign #systemdesigninterview #hld #interviewpreparation #softwareengineering #distributedsystems