Nginx Dynamic Config with Internal Domain DNS Resolution

nginx.conf.erb

server {
    listen 80;
    server_name *.<%= @domain %>;
    return 301  https://$host$request_uri;
}
server {
  listen 443 ssl http2;
  server_name 		<%= @domain %>;
  ssl_certificate       /etc/letsencrypt/live/<%= @domain %>/fullchain.pem;
  ssl_certificate_key   /etc/letsencrypt/live/<%= @domain %>/privkey.pem;
  location / {
    resolver	        192.168.1.1;
    proxy_pass         http://admin;
  }
}
server {
  listen 443 ssl http2;
  server_name		 *.<%= @domain %>;
  ssl_certificate       /etc/letsencrypt/live/<%= @domain %>/fullchain.pem;
  ssl_certificate_key   /etc/letsencrypt/live/<%= @domain %>/privkey.pem;

  if ($host ~* ^(www\.)?([^.]+).<%= @domain %>$) {
    set $subdomain $2;
  }

  location / {
     resolver	      192.168.1.1;
     proxy_pass      https://$subdomain.<%= @internaldomain %>;
  }
}