现在很多linux主机使用apache作为web服务器的，大部分是基于这个原理来配置虚拟主机的。
下面就windows下以apache 2.4.3作为演示的一个教程。
这里只是简单的说明下，简述实现的原理
1.Apache的配置文件httpd.conf，找到Virtual hosts，进行如下修改保存。
# Virtual hosts
#Include conf/extra/httpd-vhosts.conf
去掉第2行的‘#’号，改为
# Virtual hosts
Include conf/extra/httpd-vhosts.conf
这样就开启了extra文件夹下的httpd-vhosts.conf，以后修改虚拟主机只要在这个文件进行。
2.对httpd-vhosts.conf进行配置。
例如域名www.a.com和www.b.com
# Virtual Hosts
#
# Required modules: mod_log_config
# If you want to maintain multiple domains/hostnames on your
# machine you can setup VirtualHost containers for them. Most configurations
# use only name-based virtual hosts so the server doesn't need to worry about
# IP addresses. This is indicated by the asterisks in the directives below.
#
# Please see the documentation at
# <URL:http://httpd.apache.org/docs/2.4/vhosts/>
# for further details before you try to setup virtual hosts.
#
# You may use the command line option '-S' to verify your virtual host
# configuration.
#
# VirtualHost example:
# Almost any Apache directive may go into a VirtualHost container.
# The first VirtualHost section is used for all requests that do not
# match a ServerName or ServerAlias in any <VirtualHost> block.
#
<VirtualHost *:80>
ServerAdmin [email protected]
DocumentRoot "d:/www/a"
ServerName a.com
ServerAlias www.a.com
ErrorLog "logs/a.com.log"
CustomLog "logs/a.com.log" common
<Directory "d:/www/a">
Require all granted
</Directory>
</VirtualHost>
<VirtualHost *:80>
ServerAdmin [email protected]
DocumentRoot "d:/www/b"
ServerName b.com
ServerAlias www.b.com
ErrorLog "logs/b.com.log"
CustomLog "logs/b.com.log" common
<Directory "d:/www/b">
Require all granted
</Directory>
</VirtualHost>
注意：apache 2.4以上版本中需要在目录下面添加 Require all granted,否则无论怎么访问都是403。
这个我也查找了好久才查出的原因，官方文档也没有找到说明的地方。