I want to run
$ letsencrypt --apache certonly
to get a new cert, but I can't find anywhere in the documentation that explains what this actually does other than that it uses the "tls-sni-01 challenge type". What does it actually change in my Apache config, and does it delete the changes after completing the challenge? I am nervous about running a script that makes automatic changes to my Apache configuration.
If I run it on a live site will it result in any downtime?