This repository provides a Caddy configuration which can be built into a docker image.
Port 4200 serves a static html page from /caddy/index.html
Port 9000 serves a json response from /caddy/index.json
docker build .
docker run -p 4200:4200 -p 9000:9000 sha256:<sha>
You can mount some other file to these two paths to make it serve something else.