Comment 5 for bug 1346849

> I think 50x is appropriate. "Something awful happened". This was no
fault of the user. 503 would probably be the most accurate.

FWIW I disagree - something awful didn't happen, someone sent a bad request, a signal to a resource which doesn't support signals, so it's user error.

The other option would be to silently discard the request, do nothing (because there's nothing to be done) and return 200 I guess?

Or, we return 501 and say "Not Implemented", but to me that indicates the server doesn't implement the thing at all, rather than the specific resource you're trying to access doesn't?

In any case 500 is not the right response, as heat didn't have any internal error.