nginx转发请求到后台时,并发的情况下会出现nginx只用了很低的cpu转发了很少的请求到后端，应该是因为用了短连接导致大量端口被占用，所以需要改成长链接去转发。

upstream face_background {
             server 127.0.0.1:8090  max_fails=5 fail_timeout=5s;
                 keepalive 256;#必须配置的


    }
server
{
    listen 80;
    server_name face-api.xxx.cn;
    index index.php index.html index.htm default.php default.htm default.html;
    root /www/wwwroot/face-api.xxx.cn;
    
 
       location ~ / {
       
            proxy_http_version 1.1;#必须配置的
            proxy_set_header Connection "";#必须配置的
            proxy_set_header X-Real-IP $http_x_connecting_ip;
            proxy_set_header X-Real-PORT $remote_port;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

            proxy_set_header Host $http_host;
            proxy_set_header Scheme $scheme;
            proxy_set_header Server-Protocol $server_protocol;
            proxy_set_header Server-Name $server_name;
            proxy_set_header Server-Addr $server_addr;
            proxy_set_header Server-Port $server_port;
       
            proxy_pass http://face_background;
    }

}