Nginx反向代理并缓存静态文件

server { 
 listen 81; 
 location ^~ / { 
    _pass http://server.usa.com; 
    proxy_set_header       X-Forwarded-For $proxy_add_x_forwarded_for; 
    proxy_cache            STATIC; 
    proxy_cache_valid      200  10d; 
    proxy_cache_use_stale  error timeout invalid_header updating http_500 http_502 http_503 http_504; 
   } 
}