Apache的反向代理主要利用转发模块，proxy和proxy_http
先配置 Apache 支持proxy 和 proxy_http
在Ubuntu系统下，Apache的配置文件在目录/etc/apache2下，里面会看到我们需要用到的两个目录
mods-available Apache所有的模块
mods-enabled Apache所支持的模块
接下来需要进入mods-available 找到proxy.load和proxy_http.load 这两个模块，将这两个模块配置到mods-enabled
输入命令：
ln -s /etc/apache2/mods-available/proxy.load /etc/apache2/mods-enabled/proxy.load
ln -s /etc/apache2/mods-available/proxy_http.load /etc/apache2/mods-enabled/proxy_http.load
模块开通好了以后，接下来要配置一个虚拟主机，然后将虚拟主机的请求转发到指定的服务器上。
配置虚拟主机
同样也是在/etc/apache2下面有个关于虚拟主机的配置目录：
sites-available 所有可用的虚拟主机
sites-enabled 已经配置支持的主机
首先进入 sites-available 将000-default.conf拷贝并重命名为proxy.conf
编辑proxy.conf
<VirtualHost *:80>
# The ServerName directive sets the request scheme, hostname and port that
# the server uses to identify itself. This is used when creating
# redirection URLs. In the context of virtual hosts, the ServerName
# specifies what hostname must appear in the request's Host: header to
# match this virtual host. For the default virtual host (this file) this
# value is not decisive as it is used as a last resort host regardless.
# However, you must set it for any further virtual host explicitly.
ServerName example.cn 自定义的主机域名
ServerAdmin webmaster@localhost
DocumentRoot /var/www/html 指向的目录
# Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
# error, crit, alert, emerg.
# It is also possible to configure the loglevel for particular
# modules, e.g.
#LogLevel info ssl:warn
ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined
ProxyPass / http://localhost:81/ 转发的主机与端口号
ProxyPassReverse / http://localhost:81/ 如果有页面的重定向，不加此项会报错，此项正是反向代理
# For most configuration files from conf-available/, which are
# enabled or disabled at a global level, it is possible to
# include a line for only one particular virtual host. For example the
# following line enables the CGI configuration for this host only
# after it has been globally disabled with "a2disconf".
#Include conf-available/serve-cgi-bin.conf
</VirtualHost>
重启Apache，即可。