@Freakeao and @mariosipad
I just finished the transition to docker.
But I have to admit that I am not using COPS anymore.
As I had to start from scratch anyways I figured, let me check out docker, cops, calibre-content-server and calibre-web.
Finally I ended up with:
docker linuxserver/calibre-web
It does everything I need it to do and I like the, imho, more modern look and feel of it.
Docker and docker compose were actually quiet easy to grasp, but letsencrypt's certbot in combination with apache reverse proxy gave me a headache for a while. Now it works as intended.
Also, I had nvchecker in use already for other projects. Turns out it works for docker updates also. Awesome!
So far, I am really happy with everything.
Thanks a bunch guys for recommending docker to me!!
PS: @mariosipad - wish I could help you out there, but I have zero php knowledge. Before I decided to give docker a go, I looked at the php code and ...
...
gave up.