[ReactiveJelly]

https://en.wikipedia.org/wiki/Common_Gateway_Interface

The most primitive version is just launching one process per request, piping the HTTP request into stdin, and piping the response out of stdout.

It works, but you can imagine the startup latency is rough and it takes a lot of resources.

There are faster variations that try to reduce the overhead. Ironically FaaS is sort of a rebirth of CGI