[malkia]

At Google, had to do Java on borg, and used few times the "Cloud Trace" debugger (not sure how it was called), but it allowed you to watch multiple instances of your binary in production, and then add some isolated set of java statements around code blocks, this way you can say (somehow) - if you end up on this line, then "inject" (somehow) something to log out... and then you can add whatever you want to be logged (like arguments, variables around, etc.).

But then later it got scrapped, or something like it.

Cloud "debugging" when you have multiple instances is one of the cases where there is no suitable enough debugger (yet).