[MAJOR] Add a 'start_time' variable to nginx 1.4.1
to support an X-REQUEST-START header.
This header could be used to measure time of rquest spent on backend apps.
example (server sectoin): proxy_set_header X-Request-Start $start_time;
Also could be used in log ou can add in your log_format:
$upstream_response_time "$start_time" "$msec"