location / {
 proxy_set_header X-Real-IP $remote_addr;
 proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
 proxy_set_header Host $http_host;
 proxy_set_header X-Nginx-Proxy true;

 add_header Proxy-Node $upstream_addr;
 add_header Proxy-Status $upstream_status; 
 
 proxy_http_version 1.1;
 proxy_pass http://tianusa;
 }

underscores_in_headers on; （默认 underscores_in_headers 为off）