Vicidial is OS independent. More importantly WHY would you be tempted to upgrade the OS of a functional Vicidial system?
If you are into "best practices" and "update! update! upgrade!" per Microsoft and Engineering brainwashing, oops "standards based training", consider this: If you upgrade a single package on a Vicidial server and find that it breaks something, you can usually just downgrade that package and get yourself back online. But if you upgrade the OS, downgrading is often not viable without a full reinstall.
Thus OUR best practices involve whitelist lockdown and never upgrade an existing OS. However: If there arises a need to have more up-to-date systems, one would:
* Upgrade Vicidial to the latest.
* Run the new version for a few days to be sure there are no issues.
* build a fresh server with the latest Vicibox .iso installer (which will be stock, fully tested, and latest-greatest everything AND compatible since you just upgraded Vicidial even if it installs a newer version of Asterisk!). This would be a new server in your cluster
* Down the old servers as you build new ones.
This means you never have a "point of no return" panic attack when something breaks, and allows you to "upgrade! update!" to your heart's content.