nginx-buildpack

It looks like there are a few CGI crates on crates.io, but they're not super popular. Crates.io uses https://github.com/emk/heroku-buildpack-rust in combination with https://github.com/ryandotsmith/nginx-buildpack, which puts nginx in front of a Rust application server, communicating over a socket. See here: https://github.com/ryandotsmith/nginx-buildpack/blob/master/... for the default config, https://github.com/rust-lang/crates.io/blob/0f3adf36108dfac6... for the one we actually use. (Given this is offtopic, I'll leave it at that. Happy to answer questions over at https://users.rust-lang.org/ )

Sounds like they're hosted entirely on Heroku and didn't want to go through the effort of adding external infrastructure. But I just found out apparently you can host Nginx on Heroku [1] which is neat, but looks a bit sketchy [1] https://github.com/ryandotsmith/nginx-buildpack

Heroku definitely does. Even inside a single dyno. Switch to at least 2x-sized dynos and use nginx-buildpack (https://github.com/ryandotsmith/nginx-buildpack) with multi-buildpack (https://github.com/ddollar/heroku-buildpack-multi). You'll probably need to modify/fork the ruby buildpack to do asset compiles twice (if necessary) and check-in both apps into the same repo. And of course modify the nginx configuration.

If you are interested in running NGINX on Heroku, checkout my buildpack: https://github.com/ryandotsmith/nginx-buildpack