使用域名中截取的一部分 IP 作为 Nginx 的 Upstream

server.conf

server {
    listen       80;
    server_name  ~^(?<sip>([\d\.]*))\.example\.com$;

    location / {
        proxy_pass        http://$sip:9001;
        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;
    }
}