Getting the ports right with docker compose, with Caddy as reverse proxy?

Note: I've asked this on the Gramps forum, but got no reply. I would have hoped that somebody, somewhere may be using Gramps-web with Caddy, but if they are, they seem to have better things to do than answer my idiot questions!

Short version: What ports should I set in my docker compose file, given that 80 is already allocated, and that I want to use Caddy as a reverse proxy?

Longer version: I'm a bit confused about what ports to use, or to set, with Gramps-web. According to the standard docker compose file linked on the "deploy with docker" section of the installation docs, the ports for the outward facing Gramps-web container are "80:5000".

But according to the example on this github repo, for use with nginx, the ports are given as "5555:80"

I'm using Caddy as my reverse proxy and for managing TLS certificates from LetsEncrypt. I can get Gramps-web up and running if I set the ports to "8001:5000" (I can't use 80 as that's already used by Caddy), and set the Caddyfile port to 5000.

This means I can start Gramps-web, and get the page for creating a new user. But then clicking on "Submit" produces "Error: Error 500".

So something is not right, and I'm assuming that the main culprit is the ports.

Any advice would be welcome! Many thanks.

gramps-project / gramps-web

Getting the ports right with docker compose, with Caddy as reverse proxy? #525