add X-Request-Start for New Relic

srv.conf

# 1. for: https://docs.newrelic.com/docs/features/request-queuing-and-tracking-front-end-time
# 2. as some guys ask this question for haproxy (seems can not do this):
#    http://www.faultserver.com/q/answers-how-to-set-the-request-start-time-with-haproxy-447033.html
# 3. and, we can not add this header in httpd server, because it's too late..

limit_req_zone $binary_remote_addr zone=one:1m rate=1r/s;

server {
    listen 1025;

    location = /a {
        limit_req zone=one burst=2;

        set_by_lua $now ' return ngx.now() ';
        set $now2 '';
        access_by_lua ' ngx.var.now2 = ngx.now() ';

        rewrite ^ /a-real break;

        add_header X-Now "[ $now ]";
        add_header X-Now2 "[ $now2 ]";
        proxy_set_header X-Request-Start "[ $now ]";
        proxy_set_header X-Request-Start2 "[ $now2 ]";
        proxy_pass http://127.0.0.1:1025;
    }

    location = /a-real {
        echo $http_x_request_start;
        echo $http_x_request_start2;
        echo done;
    }
}

URL from 2 is now: https://serverfault.com/questions/447033/how-to-set-the-request-start-time-with-haproxy