if ( $http_user_agent ~ "dashen" ) {
 set $flag "01";
}

server
{
 listen 192.168.1.251:80;
 server_name *.example.com;
 index index.html index.htm index.php;
 charset utf-8;
 location / {
 set $flag "00";
 if ( $http_user_agent ~ "dashen" ) {
   set $flag "01";
  }
 if ( $http_user_agent ~ "mianwo" ) {
   set $flag "02";
  }
 if ( $http_user_agent ~ "bingkuai" ) {
   set $flag "03";
  }
 if ( $http_user_agent ~ "hadoop" ) {
   set $flag "04";
  }
  proxy_set_header Host $host;
  proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
  if ( $flag = "00" ){
   add_header Z-Server mobile;
   proxy_pass http://webserver_mobile;
  }
  if ( $flag = "01" ){
   add_header Z-Server dashen;
   proxy_pass http://webserver_dashen;
  }
  if ( $flag = "02" ){
   add_header Z-Server mianwo;
   proxy_pass http://webserver_mianwo;
  }
  if ( $flag = "03" ){
   add_header Z-Server bingkuai;
   proxy_pass http://webserver_bingkuai;
  }
  if ( $flag = "04" ){
   add_header Z-Server hadoop;
   proxy_pass http://webserver_hadoop;
  }
 }
}

upstream webserver_mobile{
 server 127.0.0.1:8900 max_fails=2 weight=2 fail_timeout=10s;
}
upstream webserver_dashen{
 server 127.0.0.1:8901 max_fails=2 weight=2 fail_timeout=10s;
}
upstream webserver_mianwo{
 server 127.0.0.1:8902 max_fails=2 weight=2 fail_timeout=10s;
}
upstream webserver_bingkuai{
 server 127.0.0.1:8903 max_fails=2 weight=2 fail_timeout=10s;
}
upstream webserver_hadoop{
 server 127.0.0.1:8904 max_fails=2 weight=2 fail_timeout=10s;
}