Environment variables are only applied once on first start

Hi, I use this docker registry UI and I experienced an issue when trying to deploy it on LXC with Proxmox VE.

Bug description

After a long time troubleshooting the installation and CORS headers (which I understand fairly well), I concluded that my environment variable changes were not being applied at all.

LXC inside Proxmox, as opposed to "traditional" docker tool, allow you to stop a container, and change environment variables, which I thought would be my easy way to reconfigure the container...

I only briefly looked at the code of registry-ui but it seems it may be applying some (or all) environment variables only once using sed and then store the modified (no longer a template) index.html file.

This makes changing environment variables after initial volume start not possible. I found that it was probably what was happening (and not my configurations), because I manually changed the index.html on the file system to set my registry URL properly and everything started working properly.

As a workaround, what I did is to configure a fresh container on Proxmox using the registry-ui image, make sure I don't start it, configure all my environment variables, make a snapshot (or backup), and anytime I need to change any config I rollback to this initial snapshot, make the changes, then start it again...

How to Reproduce

Configure a registry-ui using Proxmox CT container by pulling the image from registry-ui. Start the container at least once without setting any environment variables. Stop the container. Change or configure all the desired environment variables for the registry URL for example. Start the container. Nothing should work (unless you manage to have a local registry working there, but that shouldn't be the case)

Expected behavior

It would be great, and I think it would be easy to do, to change the way environment variables are applied, so that they are systematically re-read on each container start and applied properly.

System information

• OS: ProxmoxVE 9.1.5 (for hosting registry-ui and registry itself)
• Browser: Firefox latest stable as of this date running on a linux distro
• Docker registry UI:
  • Version: Docker Registry UI 2.7.0-82f6240dab
  • Server: docker
  • Docker version: lxc 6.0.5 running on proxmox VE ("out of the box" experience)
  • Docker registry ui tag: [main]
  • OS/Arch: linux/amd64
  • Tools: proxmox-ve 9