It is. We run an old version of our application on Java 6. Apparently multiple people have tried to upgrade it in the past but it proved too difficult because it's using a bunch of completely obsolete technology with little available documentation that seems to randomly break when you upgrade even minor things.

The plan has been to gradually replace it with the new version of the software (which runs on Java 17), unfortunately this plan has been ongoing for 10 years and it's not gonna be done anytime soon.

Such are the sad realities of working on legacy code sometimes.

Absolutely, so you try to seal it in hermetically, only talk to it over a special message bus or something.

Sometimes the upgrade path from 6 onwards isn't as nice as it usually is from 8 up, especially if you built with some old undead libraries that require an heroic effort to understand well enough to reimplement. Takes a very special organisation to divert some person-years to pull it off, and as some middle or other manager it's highly unlikely to catch you a new, better job even if it goes well.