配置Nginx weight出错？

Question

upstream www_data_cn {ip_hash;server 172.16.15.138:8180 weight=3 max_fails=3 fail_timeout=10s;server 172.16.15.138:8080 weight=1 max_fails=3 fail_timeout=10s;server 172.16.15.137:8180 weight=3 max_fails=3 fail_timeout=10s;server 172.16.15.137:8080 weight=1 max_fails=3 fail_timeout=10s;}重启nginx时 报错Restarting nginx: nginx: [emerg] invalid parameter "weight=3" in /etc/nginx/nginx.conf:72nginx: configuration file /etc/nginx/nginx.conf test failed 不设置weight 就可以通过，不知道为什么