CDN is an intelligent virtual network built on the basis of the existing network. Relying on edge servers deployed in various places, through the load balancing/content distribution/scheduling of the central platform and other functional modules, users can obtain the required content nearby, reduce network congestion, and improve user access response speed and hit rate; Comprehensive information such as the distance and response time of the website is requested to the nearest service node; its purpose is to enable users to obtain the required content nearby, solve the Internet network congestion situation, and improve the response speed of users visiting
websites .
Traditional access process:
(1) After the user enters the www.baidu.com domain name, the OS will query the IP address of the domain name
from LocalDNS (local domain name server); (2) If the local domain name server does not find it, the local domain name server LocalDNS will query the root domain name server (RootDNS) for the authoritative server of the domain name; (3) RootDNS will respond to LocalDNS after obtaining the domain name authorization DNS record; (4) LocalDNS will respond to the obtained domain name ip address to the client; After that, visit the site server; (6) The site server responds to the request and returns the content
to
the
client
.
CDN access process:
(1) 用户输入 www.baidu.com 域名后, OS 会向 LocalDNS(本地域名服务器) 查询域名的 ip 地址;
(2) 如果本地域名服务器中没有查询到, 本地域名服务器 LocalDNS 就会向根域名服务器(RootDNS)查询域名的授权服务器;
(3)RootDNS 得到域名授权 DNS 记录后, 回应给 LocalDNS;
(4) LocalDNS 得到域名的授权 DNS 记录后, 继续向域名授权 DNS 查询域名的 ip 地址;
(5) 域名授权的 DNS 查询域名记录后, 回应给 LocalDNS;
(6) LocalDNS 得到域名记录后向智能调度 DNS 查询域名的 ip 地址;
(7) 智能调度 DNS 通过一定的算法和策略将最合适的 CDN 节点 ip 地址回应给 LocalDNS;
(8) LocalDNS 将得到的域名 ip 地址并回应给用户端;
(9) 用户端得到域名 ip 地址后访问站点服务器;
(10) CDN 节点服务器应答请求, 将内容返回给客户端; 缓存服务器一方面在本地进行保存, 另一方面把获取到的数据返回给客户端, 完成数据的服务过程.
Summarize
- The principle of CDN is to use various cache servers and distribute these cache servers in areas or networks where user access is relatively concentrated;
- The basic idea of CDN is to avoid links on the Internet that may affect the speed and stability of data transmission as much as possible, so as to make content transmission faster and more stable. A layer of intelligent virtual network based on the existing Internet is formed by placing node servers throughout the network;
- In short, CDN is a distributed cache server, which stores a lot of files and is distributed all over the world, so that everyone can access them nearby.