Pi-hole by default installs lighttpd as its web-server. This lighttpd server usually handles and web traffic to Port 80, and the admin dashboard for pi-hole can be accessed using the IP of the device it is installed on, such as http://192.168.1.25/admin/.

But with NginX installed onto this device, means that it is actually NginX that would process any web traffic to Port 80; and therefore this would result in a conflict in that lighttpd would not be able to process Port 80 as well.

The solution is to keep lighttpd running on an alternate port (such as 81) and let NginX proxy all requests to pi-hole to that port.

/etc/lighttpd/lighttpd.conf

...
server.port                 = 81
...

sudo systemctl restart lighttpd.service

Check lighttpd is running

sudo systemctl status lighttpd.service

/etc/nginx/sites-available/pi.hole

server {
  listen 80;
  listen [::]:80;
  server_name pi.hole;
  return https://$host$request_uri;
}
 
server {
  listen 443 ssl http2;
  listen [::]:443 ssl http2;
 
  server_name pi.hole;
 
  ssl_certificate 'ssl/pi.hole.crt';
  ssl_certificate_key 'ssl/pi.hole.key';
 
  location / {
    proxy_pass http://localhost:81;
    include proxy.conf;
  }
 
  # let's go directly to the login page
  location = / {
    return $scheme://$host/admin/index.php?login;
  }
}

The proxy.conf file:

proxy.conf

proxy_set_header Host $http_host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;

sudo systemctl restart nginx.service

Check NginX is running

sudo systemctl status nginx.service

Whenever someone visits https://pi.hole, it redirects to https://pi.hole/admin/index.php?login which is the login page for pi-hole admin dashboard.

https://www.tinywp.com/pi-hole/