Best practice for single cert covering multiple subdomains on different servers?

Say I have

On Server A, and

On Server B, and

on Server C

Not all running the same server software and not all running a webserver. How do I include all relevant subdomains in one certificate in this case?

I think the easiest would be using DNS, since you don’t have a webserver on all the servers.

Cool, and that feature isn’t implemented into the letsencrypt client yet, is that correct? Assuming I use this to track the progress

correct. It is already in some of the alternative clients though. I’m not fully sure which of the clients include the DNS option, but certainly and do.

Great, thanks for the help!