Should I change the default FQDN in Ubuntu 18.04 for generating certificates?

I'm using this article to create an image registry for installing OKD on an airgapped environment, which will be used to pull the necessary installation images and move them to the new environment using physical media for installation. It calls for creating

the self-sign CA, server certificate with both the short and fully qualified hostname of this VM

the VM being Ubuntu 18.04. It seems to me that the default fully qualified hostname for Ubuntu 18.04 is just ubuntu. I've tried verifying this with hostname --fqdn as well as checking in /etc/hostname.

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I believe the only time any connection outside of the local network needs to be established is when pulling the image files from the OKD repository. So my question is, is this FQDN adequate for my purposes? Is it alright for me to prepare the server certificate with just "ubuntu" as the FQDN? Or should I update it to something else? Thanks!