Creating a poll that doesn't crash under load

I was hired to create a poll that would run during an audience show at the Nerdland Festival this weekend. The poll ran during one of the headlining shows in a tent with a 3.5K capacity. During the show the hosts showed a QR code on the big screens, which got scanned by loads of people in the audience, and they all voted at exactly the same time. The obvious solution My first reaction after getting the briefing was: simple, some serverless hosting (Vercel or Cloudflare), backed by some light database in the cloud (like Turso or D1). I settled on the Cloudflare route and went to work. Everything looked fine, and I was nearly ready to deliver the project when I ran a final load test using this free tool and quickly discovered that we had a problem. 250 requests per second, 26% success rate Under sustained load of 250 simultaneous requests per second the app would start returning 500 errors, and the requests that got through started taking a very long time. The reason was simple: the…