Lesson 1: What breaks first when traffic grows tenfold
30 min read·
Module 14 · Lesson 1 · About 50 minutes · Needs: Module 3 lessons 1 and 3 (peak RPS, index sizing), Module 1 lesson 2 (statelessness), Module 7 lesson 3 (parallelism). No key and no model calls
The situation
Week 14. Gareth asks step 10 of the design order: what would you revisit at ten times the scale? Funmi wants to know what fails first; Ana, what it costs to stop it.
The running example is the busiest five minutes in the shared data, Monday 28 September 2026 at 13:25 UTC: 51.6 Ask requests a second (RPS) at Joel's target. This lesson replays it at ten times, and replays Tallis Retail Group's onboarding to see who pays when one tenant grows.