NGINX - Proxy the Request from VPS to Root Server

Question

I would like to use my VPS as a proxy. That means if I call the VPS IP 123.123.123.123 the VPS should forward the request to my proper dedicated server (for example 444.444.444.444) without seeing the Root Server IP in the browser.

I had the code a long time ago - but I do not have the file anymore. Could someone help me which lines I have to insert?

server {
        listen 123.123.123.123:80;
        server_name  example.com;
        rewrite ^(.*) http://www.example.com$1 permanent;
}

server {
        listen 123.123.123.123:80;
        server_name www.example.com;

        location ~ \.php$ 
        {
            include snippets/fastcgi-php.conf;
            fastcgi_pass 127.0.0.1:9000;
        }

}