As many know, one thing I've wanted in httpd's proxy for http is a sort of pre-request ping option (ala what we have for ajp) and nothing ever worked out fine, for a variety of reasons.
Anyway, I've gone back to an idea I had a long while ago and one which ACO and Filip Hanik and I have played around with and it's very simple: for backends which are http/1.1, simply use a 100-Continue. If the backend is alive (and compliant) we should semi-immediately continue with the request, otherwise we can assume it's down (or so loaded that it times out) and choose another backend. I'd like to get this in 2.3.7 before I T&R it, and it will be optional behavior, not the default, but wanted to give people a head's up beforehand.
