https://onlineornot.com is "just" a Next.js app with a database that calls a lambda function over a million times a week (website/API monitoring).
There's also a slightly more complicated part that runs a Chrome browser to check React/JS SPAs.
There's also a slightly more complicated part that runs a Chrome browser to check React/JS SPAs.
On top of that, there's a bit of replication across regions (and soon across cloud vendors), so if an entire AWS region goes down (happened twice last month), the checks keep on checking.