I have my angular app installed at nginx on my ip ,so whenever I put my ip xx.xxx.xxx in browser static content of my angular app is served ,Now I want to have the reverse proxy for the same ip as load balancer to my backend node app server

My configuration

upstream app_servers {
    server 127.0.0.1:3900;
    server 127.0.0.1:3901;
    server 127.0.0.1:3902;
    server 127.0.0.1:3903;
}

server {
    listen 80;
    server_name xx.xxx.xxx; // ip
    location / {
        proxy_set_header   X-Real-IP $remote_addr;
        proxy_set_header   Host      $http_host;
        proxy_pass         http://app_servers;
    }
}

Now if use above configuration my load balance works properly but my angular app doesn't gets delivered .Any idea how to do both simultaneously .I know I can giver different server name ,but any idea to do this with only ip ,currently I dont have and domain.

Thanks