How I built a flash-sale engine that can't oversell

I created this piece of content for the purpose of entering the H0: Hack the Zero Stack hackathon. #H0Hackathon

The problem (that's harder than it sounds)

"Don't sell more tickets than you have" sounds trivial until 10,000 people click Buy in the same second.

The naive fix — a single remaining counter you decrement on every purchase — falls apart under load. And when you try to go multi-region, it gets worse: with eventual consistency across regions you can oversell during the replication window.

I wanted a flash-sale engine that is globally fast AND strongly consistent AND operationally simple — all three. That combination is precisely what Amazon Aurora DSQL is built for, so I built DropZero on it for the hackathon.