Below is a question I originally posted on Stack Overflow. Feel free to respond there if you use that site:
http://stackoverflow.com/questions/4272686/nginx-is-it-possible-to-capture-response-headers-in-access-log-when-using-nginx

Hi,

We are using nginx as a reverse proxy to control and log access to a Clojure (Java) web service application.

We are able to generate an access_log and capture incoming headers using nginx just fine. Our Clojure app logs activity via log4j. Trouble is, is that we can't match an entry in the access_log to an entry generated by the app.

The app responds to access by sending response headers as well as a body. We can freely change these response headers. My initial thought was to generate a UUID that corresponds to each and every web service request and send that back to the user within the reply header X-Uuid. My thought was that I could capture this response by creating a custom log_format:

log_format lt-custom '$remote_addr - $remote_user [$time_local] '
'"$request" $status $body_bytes_sent '
'"$http_referer" "$http_user_agent" $request_time $http_x_uuid';

It's looking like nginx can capture headers in incoming requests but not outgoing replies (I verified this by replacing $http_x_uuid with $http_content_type).

So! Is there a way I can tie my access_log enties and my log4j entries by capturing outgoing reply headers using nginx? Is there a better way? I'd rather not have to rely on users generating their own UUIDs.

Thanks so much!