Unable to add `$upstream_addr` to a response header field

[michalrus@…]

Whenever $upstream_addr is added to any header field with add_header, that field is missing from responses:

    location {
      proxy_pass http://some_upstream;

      # This works (so request phase should be fine?):

      add_header  X-Upstream-Content-Type $upstream_http_content_type;

      # This doesn’t:

      add_header     X-Upstream-Addr $upstream_addr;    
    }

How can this be achieved?

Thank you!

[Maxim Dounin]

Works fine here, including the long obsolete 1.15.8 version of nginx. Test configuration:

server {
    listen 8080;

    location / {
        proxy_pass http://localhost:8081;
        add_header X-Upstream-Addr $upstream_addr;
    }
}

server {
    listen 8081;
    return 200 ok;
}

Testing with curl:

$ curl -I http://127.0.0.1:8080/
HTTP/1.1 200 OK
Server: nginx/1.15.8
Date: Mon, 19 Apr 2021 14:21:05 GMT
Content-Type: text/plain
Content-Length: 2
Connection: keep-alive
X-Upstream-Addr: 127.0.0.1:8081

Please test if you are able to reproduce the problem with vanilla nginx, not a modified fork you are using. If you are able to, please provide additional details, such as full configuration you are using, and test output which demonstrates that the header is not added.

[Maxim Dounin]

Feedback timeout.