Challenge 3: A Nested Location Block Losing Its Parent's Headers — Solution Walkthrough

What actually happens:

Per this chapter's own warning box, because the location /api/ {}
block sets its own proxy_set_header (for X-Api-Version), it stops
inheriting every proxy_set_header from the parent server {} block
entirely — not just the headers it doesn't mention. Both
X-Forwarded-For and X-Forwarded-Proto silently disappear from any
request handled by /api/, even though neither was ever explicitly
removed or overridden — they're simply no longer inherited once this
location block has any proxy_set_header of its own.

Why this is easy to miss:

There's no error, warning, or visible sign that this happened — the
config still looks correct on a casual read, since X-Forwarded-For and
X-Forwarded-Proto are never mentioned or contradicted anywhere inside
the /api/ block. The only way to notice the problem is knowing about
this specific Nginx inheritance behavior in advance, or discovering it
after the fact when the backend behind /api/ starts misbehaving in
ways that trace back to missing forwarded headers.

The fix:

Explicitly repeat every header still needed inside the /api/ block
itself:

  location /api/ {
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header X-Forwarded-Proto $scheme;
      proxy_set_header X-Api-Version "2";
      proxy_pass http://backend_pool;
  }

WHY THIS WORKS AS AN ANSWER
------------------------------
This exercise directly applies this chapter's own warning box to a
concrete two-block config, correctly identifying that ALL parent
headers are lost, not just the newly added one, and that the fix is
explicit repetition rather than assuming partial inheritance still
applies.