<<so I don’t want to install the nginx container in the sample compose either>> Thought the same initially but it turned out both nginx instances are required. I have a working setup with an installed nginx instance + certbot and an almost unmodified docker-compose.yml The modifications I made were changing container names (so they fit my standard) and the http port

The lemmy documentation https://join-lemmy.org/docs/administration/install_docker.html recommends the following location block for the installed nginx:

  location / {
       proxy_pass http://localhost:LEMMY_PORT;
       proxy_set_header Host $host;
       include proxy_params;
}

This did not work for me! I had to comment the proxy_set_header line to make things work. With it I run into an error 400.

Please do add a tag to your post as stated on the sublemmy sidebar! Thank you. :)

Here's how I setup mine https://lemmy.dcrich.net/post/1150

It's better to go ahead and install the nginx container as the config will handle all the backend stuff and all you have to do is forward port 80 in NPM