I need to make sure a file actually exists before proxy_pass-ing the request to an upstream server. I don't serve existing files directly using Nginx because there are some application-specific logic i need to perform on the application server for such requests.

I've looked at try_files, but it seems like it will serve the file straightaway once it is found, which is not what I want here. Another way is to use if (!-f $request_filename), but as mentioned here: http://wiki.nginx.org/Pitfalls#Check_IF_File_Exists, it's not a terrible way to check the existence of a file.

Is there a feasible yet efficient way?