events {}

http {
    upstream backend_servers {
        server FWD_server:7443;
    }

    server {
        listen 7443;

        location / {
            proxy_pass https://backend_servers;
            
            # --- Standard Proxy Headers (Sent to App) ---
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;

            # --- NEW: Custom Response Header (Sent to User) ---
            # This adds a header named 'X-Server-IP' to the response you receive.
            # $upstream_addr holds the IP:Port of the actual container that served the request.
            add_header X-Server-IP $upstream_addr always;
        }
    }
}