Anyone have thoughts on why the hostname of my k3s cluster node change from the FQDN it started with to it’s shortname after an outage? Or vice versa?

That is not something k3s would have any influence over

check /etc/hostname, that's where it actually lives. You can edit the file and reboot to add your domain name back.

Bill is correct, that is the difference. Thanks for closing that loop for me. I knew k3s just “referenced” something but I wasn’t 100% sure what that was. Thank you both.

I'd be shocked if k3s had anything to do with it. If your uptime's large it could've been changed anywhere between now & your previous reboot. You can also change it with the hostname command I think, and most distros have their own other commands to change as well.

Yeah we had an outage and I figured it was some combination of local configuration files and DNS. /etc/hosts was correct, /etc/hostname was not