Feature Request: Support for Nginx-like Fallback Server

[Saeid008]

Hello AdGuardHome Team,

First of all, thank you for the great work on AdGuardHome — it's an excellent tool for DNS-level protection and filtering.

I'd like to request a feature that enables AdGuardHome to act similarly to Nginx when it comes to handling unmatched or fallback requests.

In Nginx, we can define fallback behavior using blocks like:

server {
        listen 80;
        listen [::]:80;
        server_name EXAMPLE.COM;
        if ($host = EXAMPLE.COM) {
                return 301 https://$host$request_uri;
        }
        return 404;
}
server {
        listen       1001 proxy_protocol;
        listen       1002 http2 proxy_protocol;

        server_name  EXAMPLE.COM;

        root         /var/www/html;

        set_real_ip_from 127.0.0.1;
        location / {
                default_type application/json;
                return 200 '{"code":"1", "message": "Not Found"}';
        }
        #return 301 https://ip.gs;

        add_header Strict-Transport-Security "max-age=63072000" always;

 }
}

This is useful in environments when a specific port is occupied. like we can use two services in same port 443 or etc... allow proxying unmatched requests to an external fallback service (similar to Nginx reverse proxy).

This feature would be especially useful when AdGuardHome is placed behind a reverse proxy or used in multi-purpose edge setups in countries where GFW present.

Also I knew that Fallback can't use UDP so it's not supported QUIC however for DOH it's should be fine since DOT occupied port 853.

Please consider adding this to the roadmap if feasible. I’d be happy to help with testing or clarifying the use case further.

Thanks again!
Best regards.
Saeid