问Nginx反向代理显示默认页面，而不是远程主页

EN

Nginx IP : 52.2.2.2
Remote Ip : 52.2.2.3

Browser 
http://52.2.2.2/admin_portal

IP changes in Broswer
http://52.2.2.3/admin_portal

   upstream backend {
      server 10.128.0.2;
   }
   # This server accepts all traffic to port 80 and passes it to the upstream. 
   # Notice that the upstream name and the proxy_pass need to match.
   server {
      listen 80;
      listen [::]:80; 
      location / {
          proxy_pass http://backend;
      }
   }

user  nginx;
worker_processes  1;
error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;
events {
    worker_connections  1024;
}
http {
    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';
    access_log  /var/log/nginx/access.log  main;
    sendfile        on;
    #tcp_nopush     on;
    keepalive_timeout  65;
    #gzip  on;
    include /etc/nginx/conf.d/*.conf;
}