When you first use letsencrypt, or certbot, to add an SSL certificate to a Ubuntu or other linux flavour server it will often install the certificate as a standalone certificate. This could have been because of the guide you followed in the past or you may have an old server that you administer that has standalone certificates in place.
Standalone certificates specifically spin up their own web server in order to check the domain and run through the challenges and install the certificate. This can cause issues when another web server such as Apache or Nginx are already running on port 80 (http) and mean more complex renewal processes need to happen where Nginx needs to be [...]
