为什么视频网站必须使用CDN？

众所周知，视频是互联网中最耗带宽的传输形式，由此，视频网站对视频服务器带宽的需求是非常高的，

但一台服务器能够承受的访问量、能够提供支撑的带宽是有限的，因而，视频网站必须使用CDN对视频服务器进行分流减负。

什么是CDN呢？CDN，即是内容分发网络，通过在网络各处放置节点服务器构成在现有互联网基础上的智能虚拟网络，

使访客就近取得服务器上所需内容，有效解决网络拥挤等问题。

搭建视频网站CDN一般是由缓存服务器与内容分发服务器两种服务器构成。缓存服务器（CDN节点）分布于世界各地，

通过策略存储相关的视频内容；内容分发服务器则是将视频服务器上的视频内容根据一定策略分发到各个缓存服务器上。

举个简单的例子：当视频网站需要发布新视频时，视频服务器首先会将视频内容发送到CDN的内容分发服务器上，

然后由该内容分发服务器会根据设定好的策略将视频内容发送到CDN各地缓存服务器上。当用户点击视频网站的视频时，

视频网站会与CDN网络配合，根据用户地理位置（在哪里）、网络情况（电信、联通）为用户找到最好的缓存服务器。

当然，视频网站使用CDN不仅能够减少视频服务器对带宽的需求，也能有效解决电信与联通不互通问题，

以及隐藏真实的IP地址，保护视频服务器不受到攻击。

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