I have backend web servers that receive requests by way of haproxy-nginx-fastcgi. The web app used to see multiple ip's coming through in the X-Forwarded-For header, chained together with commas (most original IP on the left). At some point in the recent past (just noticed, so not sure what caused it) something changed, and now I'm only seeing a single IP passed in the header to my web application. I've tried with haproxy 1.4.21 and 1.4.22 (recent upgrade) with the same behavior. Haproxy has the forwardfor header set: option forwardfor Nginx fastcgi_params config defines this header to be passed to the app: fastcgi_param HTTP_X_FORWARDED_FOR $http_x_forwarded_for; Anyone have any ideas on what might be going wrong here? EDIT: I just started logging the $http_x_forwarded_for variable in nginx logs, and nginx is only ever seeing a single IP, which shouldn't ever be the case, as we should always see our haproxy ip added in there, right? So, issue must either be in nginx handling of the variable coming in, or haproxy not building it properly. I'll keep digging... EDIT #2: I enabled request and response header logging in HAProxy, and it is not spitting anything out for X-Forwarded-For, which seems very odd: Oct 10 10:49:01 newark-lb1 haproxy[19989]: 66.87.95.74:47497 [10/Oct/2012:10:49:01.467] http service/newark2 0/0/0/16/40 301 574 - - ---- 4/4/3/0/0 0/0 {} {} "GET /2zi HTTP/1.1" O Here are the options i set for this in my frontend: mode http option httplog capture request header X-Forwarded-For len 25 capture response header X-Forwarded-For len 25 option httpclose option forwardfor EDIT #3: It really seems like haproxy is munging the header and just passing on a single one to the backend. This is fairly impacting to our production service, so if anyone has an ideas it would be greatly appreciated. I'm stumped... :(