I am creating a proxy for my server using nginx and I want to ensure that the proxy_pass server IP is hidden from anyone trying to discover it. Based on the following server {} entry is it possible to discover xxx.xxx.xxx.xxx address?

server {
    listen 80 default_server;
    listen [::]:80 default_server ipv6only=on;

    root /usr/share/nginx/html;
    index index.html index.htm;

    # Make site accessible from http://localhost/
    server_name localhost;

    location / {        
        proxy_pass http://xxx.xxx.xxx.xxx;  // Is this hidden?      
        proxy_redirect off;
        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;                
    }

}