It's not unlimited scale, it was just over 700_000 people according to https://news.ycombinator.com/item?id=32320697. If your web page is 100 kilobytes, which seems like the maximum that would be reasonable, that's 70 gigabytes of traffic. AWS charges US$0.09 per GB so this is US$7. If you eliminate the cloud premium it's closer to US$1.

In fact loading their home page takes 3.1 MB for me over two minutes. Searching for a flight (AAL301 in this case since SPAR19 has already landed) brings this to 3.8 MB. At this size it would be 266 gigabytes, US$27. Reloading the page, I see that this was about 180 HTTP hits, though a lot of those were ads (I guess they have a way to monetize the traffic) which were blocked by uBlock Origin.

But doesn't it take a lot of CPU and RAM to serve 700_000 page views, especially at 180 hits per page view? That's 126 million hits, after all! Well, of course you can write your code arbitrarily inefficiently. According to https://crozdesk.com/software/fastly/pricing Fastly charges US$0.0075 per ten thousand hits, so if you could serve all those hits from Fastly it would cost you just under US$100. And probably if you're getting 700_000 people looking at the same thing you should figure out how to make all those hits cacheable either in Fastly or in something slower but cheaper. This probably isn't the first popular flight on FlightRadar24, even if it's the first one that's this popular.

(Also though you probably don't need 180 hits to serve up a single page. One for HTML, one for JS, one for CSS, one for an icon sprite sheet, and maybe half a dozen map tiles. The cause of death was a self-inflicted wound.)

What if we want to know the minimal CPU cost to serve up 126 million hits rather than the minimal dollar cost for someone else to serve them up for you? Well, one weekend a few years ago I wrote a static file HTTP web server called httpdito-386: http://canonical.org/~kragen/sw/dev3/server.s (docs in http://canonical.org/~kragen/sw/dev3/httpdito-readme). It's 710 lines of code and can handle 20_000-30_000 hits per second on my ten-year-old laptop (8 cores) and push about 1.8 gigabits per second of traffic. It's not the most efficient web server (it forks a new process for every connection and drops the connection after handling the first request) but it's probably adequate to get a ballpark figure.

Serving up 126 million hits with httpdito would take 84 minutes on my ten-year-old laptop, so probably you'd have needed 2-5 server machines, or one machine that wasn't ten years old. Serving up 70 gigabytes in a smaller number of hits would have taken 5 minutes.

Of course, the whole point of FlightRadar24 is that it's giving you dynamically updated Comet information about where flights are, not just serving up precomputed files from the filesystem. You could implement this kind of functionality by polling, but using Comet would probably be more efficient. Maintaining 700_000 open connections is easily within the capacity of a single server today; we were doing several thousand on our Comet server at KnowNow in 02000, using what we called RUTH (Robert's Ugly Thttpd Hack), using select() on a 32-bit machine with a gigabyte of RAM and a gigahertz.

https://news.ycombinator.com/item?id=32319147 says, "Use one big server." The associated article https://specbranch.com/posts/one-big-server/ profiles the servers they use at Azure: two 64-core CPUs with a 2-2.5 GHz clock, 4-6 instructions per clock, 256 MiB (MB?) of L3 cache, and 1 TiB (TB?) of RAM. From the cloud pricing they're citing, buying one probably costs about US$15k, roughly the cost of one programmer-week. According to https://news.ycombinator.com/item?id=32321406, FlightRadar24's revenue in 02021 was US$25M, so this would be a little less than 6 hours of their revenue.

There's no excuse.