proxy_cache seems not working with X-Accel-Redirect

[bdesemb]

I made a diagram to be more specific. It's not a problem if the client ask
for /data and get an older version of the file. The invalidate option in
proxy_cache is enough for me.

Here is my diagram without cache: http://imgur.com/a/soq69

Obviously, I don't want to reach the upstream server every time but only if
the file hasn't been reached after x minutes.

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,241734,271962#msg-271962