Intermediate
Checkout that never waits
During flash sales, orders arrive in bursts and the payment step is slow. Accept every order instantly, process them reliably, and never charge a customer twice.
All order writes can be processed asynchronously. A flash sale at 18:00 triples traffic for 30 minutes.
What your design must achieve
- Availability ≥ 99.9 %
- Writes p99 < 150 ms
- Worst queue lag < 900 s
- Duplicated side effects = 0