Challenge 1: The Three Forwarding Headers — Solution Walkthrough

The configuration:

  proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
  proxy_set_header X-Forwarded-Proto $scheme;
  proxy_set_header X-Forwarded-Host $host;

Why each line works:

X-Forwarded-For uses $proxy_add_x_forwarded_for specifically (not
$remote_addr alone) so that if the request already passed through
another proxy earlier, the current client's IP is appended to the
existing chain rather than overwriting it. X-Forwarded-Proto uses
$scheme, Nginx's own variable holding whether the original request
was http or https. X-Forwarded-Host uses $host, preserving the
original Host header the client actually requested, in case Nginx's
own internal request to the backend uses a different hostname.

WHY THIS WORKS AS AN ANSWER
------------------------------
This exercise is a direct, hands-on application of all three of this
chapter's own header examples together, correctly using
$proxy_add_x_forwarded_for rather than a plain IP variable for the
first header, which is exactly the detail that matters once more than
one proxy hop is involved.