Excellent post, good technical content, amazing feat.

That said, I echo that the amazing feat is that they can fit modern inefficient tool choices with poor mechanical sympathy into that budget. The last decade of web-dev tooling has been pushing the TCO of systems through the roof and this post is all about how to struggle against that whilst using those tools.

If they went old-school they'd get another order of magnitude savings. Many veterans know of systems doing 10x that in 10x less cost. Remember C10K was in 1999.