How to add a response header on nginx when using proxy_pass?

Question

I want to add a custom header for the response received from the server behind nginx.

While add_header works for nginx-processed responses, it does noth

Answer 1

As oliver writes:

add_header works as well with proxy_pass as without.

However, as Shane writes, as of Nginx 1.7.5, you must pass always in order to get add_header to work for error responses, like so:

add_header  X-Upstream  $upstream_addr always;