Thanks. So by deplyoing them all at once, as one unit, you avoid having to deal with the huge pain of backwards/forwards compatibility.

But what would happen if 1 of them failed to start? Or start, but immediately fail its tasks? Then you would have to revert all of them, at the same time, after some has already run for a short while, potentially writing data on the new format (for example). So I guess you can't avoid the problem with backwards compatibility completely..

Or, I guess, more realistically, you wouldl try to fix the failing service fast, without rolling back anything :)