Catch all rule - route all unmatched domains to a catch all service? Letsencrypt?

[WLun001]

How to setup a catch-all-router?

This will really depend on the other router rules that you have. Read over routers priority You will now know that you can create a PathPrefix(`/`) rule with a set priority set to a low value of 1. All your other routing rules would be processed before this one. Connect this router to a redirectRegex middleware

In addition to this, for the TLS, i would suggest to issue a wildcard certification *.mynewdomain.com, so it works over all your subdomains.