So I've been seeing lots of "proxy: error reading status line from remote server" by mod_proxy lately. Usually this is caused by the race condition between checking the connection state and the backend closing the connection due to the keep-alive timeout. As Covener pointed out to me in IRC, using mod_proxy_http's env variable "proxy-initial-not-pooled" does offer a solution to the problem albeit at the cost of performance.
The call to ap_proxy_http_process_response() in mod_proxy_http.c eventually boils down to ap_rgetline_core() which calls ap_get_brigade() on r->input_filters. This looks to me like a simple input filter might do the trick if it only checked for a possibility to read on the socket and reopens the connection upon failure type "reset by peer". I took a short look at core_create_proxy_req() in server/core.c to see how connections are set up and I wonder if it's possible to recreate/reuse that logic in an input filter. If so, this input filter would offer a nice alternative if hard coding this behavior into mod_proxy/core is frowned upon. Simply make the filter dependant on an env variable, just like proxy-initial-not-pooled.
