Their proxy seems to just be nginx, I'm surprised they didn't just share nginx or apache configurations. Most people with a box suitable for running this are probably already running a web server, so there's no reason they should be proxying from their existing web server to this dockerized server which just proxies to Signal.

Looking into their repo, they also appear to be building an nginx image from docker.io/ubuntu:20.04 instead of using docker.io/nginx. They are also running two separate nginx processes. I wonder how they ended up with this weird intricate setup.

I would be glad to help if they offered straightforward instructions.