为什么nginx每次都转到同一个tomcat上？

每次调用只看到第一个tomcat控制台有日志输出，能不能随机的啊
Engix配置如下：
`worker_processes 1;
events {

worker_connections  1024;

}
http {

include       mime.types;
default_type  application/octet-stream;
   sendfile        on;
    keepalive_timeout  65;
    upstream backend{
               server localhost:8080 weight=5;
               server localhost:8081 weight=5;
              ip_hash;
     }
server {
    listen       800;
    server_name  localhost;
    location / {
        root   html;
        index  index.jsp index.html index.htm;
 proxy_pass                  http://backend; 
       proxy_redirect              off;
       proxy_set_header            Host $host;
       proxy_set_header            X-Real-IP $remote_addr;
       proxy_set_header            X-Forwarded-For $proxy_add_x_forwarded_for;
       client_max_body_size        10m;
       client_body_buffer_size     128k;
       proxy_connect_timeout       1;
       proxy_send_timeout          300;
       proxy_read_timeout          300;
       proxy_buffer_size           4k;
       proxy_buffers               4 32k;
       proxy_busy_buffers_size     64k;
       proxy_temp_file_write_size  64k;
    }
          error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   html;
    }

}`