作用：提高吞吐量
    keepalived： 设置长连接处理的数量
    proxy_http_version：设置长连接http版本为1.1
    proxy_set_header：清除connection header 信息

    1. upstream tomcats {
    2. #       server 192.168.1.173:8080 max_fails=2 fail_timeout=1s;
    3.         server 192.168.1.190:8080;
    4. #       server 192.168.1.174:8080 weight=1;
    5. #       server 192.168.1.175:8080 weight=1;
    6.         keepalive 32;
    7. }
    8. server {
    9.         listen       80;
    10.         server_name  www.tomcats.com;
    11.         location / {
    12.             proxy_pass  http://tomcats;
    13.             proxy_http_version 1.1;
    14.             proxy_set_header Connection "";
    15.         }
    16.     }