查看/var/log/apache/error.log
日志警告：
[warn] proxy: No protocol handler was valid for the URL /. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.
处理方法：
a2enmod proxy proxy_ajp proxy_balancer proxy_connect proxy_ftp proxy_http
原文：https://blog.51cto.com/mengix/2372590