NGinx - Count requests for a particular URL pattern

You can use the post_action directive to trigger a sub_request after the main request is complete.

Useful for the sort of logging you have in mind.

** OCT 2016 UPDATE **

The post_action directive has been removed from the Nginx documentation and while it still appears to work, usage is inadvisable. Caveat Emptor!

** JAN 2020 UPDATE **

The Mirror Module, introduced in Nginx 1.13.4, essentially replicates the post_action directive.