Interesting.

Most of the stuff I've done for reverse proxies has been pretty straightforward and just using the stuff built into Nginx, but I have to admit that it wouldn't have even occurred to me to use FastCGI if I needed something more elaborate.

I used FastCGI a bit about ten years ago to "convert" some C++ code I wrote to work on the web, but admittedly I haven't used it much since then.