Then it finds the compose file based on the app name. It templates in the domain name wherever needed in the compose file, and if it's meant to be public it'll setup a nginx config (which runs on the host, not in docker). If the folder with the compose file has a backup.sh and restore.sh it also copies those over, and sets up a cron for the backup schedule. It's less than 70 lines of yaml, plus some more for restart handlers.
The only bit that irks me is the initial tls/ssl setup. Certbot changes the nginx config to insert the various certificates, which then makes my original nginx config out of date. I really like nginx and have used it for a long time so feel comfortable with it, but I've been considering traefik and caddy for a while just to get around this.
Although another option for me is to use a cloudflare tunnel instead, and then ignoring certificate management altogether. This is really attractive because it also means I can close some ports. I'll have to find some time to play around with traefik and caddy first though!
I'm sure there's something smarter I can do, like reading back the result afterwards or someting and altering my local file. But honestly, once nginx is configured for an application, I almost never touch the config again anyway.
I suspect I'm more likely to move everything over to cloudflare tunnels and ditch dealing with ssl locally altogether at this point.