Domain name analysis and CDN principle

The process by which a user accesses a Web site that does not use CDN is:

1), the user to the browser to provide access to the domain name;

2), the browser calls the domain name analytic function library to parse the domain name, obtains this domain name corresponding IP address;

3), the browser uses the obtained IP address, the Domain Name Service host sends the data access request;

4), the browser based on the data returned by the domain name host to display the content of the Web page.
The access process for a Web site using CDN cache becomes:

1), the user to the browser to provide access to the domain name;

2, the browser calls domain name Analysis Library to resolve the domain name, because the CDN to the domain name analysis process has been adjusted, so the analytic function library generally obtains is this domain name corresponding CNAME record, in order to obtain the actual IP address, the browser needs again to obtain the CNAME domain name to parse obtains the actual IP address In this process, the use of global load balancing DNS resolution, such as based on geographical information to resolve the corresponding IP address, so that users can visit nearby.

3, the resolution of the CDN cache server IP address, the browser to obtain the actual IP address, the cache server to send access requests;

4, the cache server according to the browser to provide access to the domain name, through the cache internal private DNS resolution to obtain the actual IP address of this domain name, and then by the cache server to the actual IP address to submit access requests;

5, the cache server from the actual IP address to get content, on the one hand, save in the local, for later use, two aspects of the data obtained back to the client, the completion of the data service process;

6, the client obtains the data that is returned by the cache server and then completes the entire browsing data request process.

The main technical means of implementing CDN is cache and mirror server. Can work in DNS resolution or HTTP redirection in two ways, through the cache server, or offsite mirror site to complete the transfer of content and synchronization updates

CDN Network architecture mainly consists of two parts, divided into the center and the edge of two parts, the center refers to the CDN Network Management Center and DNS Redirect resolution Center, responsible for global load balancing, equipment system installed in the Management Center room, the edge mainly refers to the remote node, CDN distribution carrier, mainly by the cache and load balancer components.

When the user visits the website that joins CDN service, the domain name resolution request will finally give the global load balanced DNS to handle. Global load Balancing DNS provides users with the node address that is closest to the user by a predefined set of policies, enabling users to get fast service. At the same time, it also maintains communication with all CDNC nodes distributed around the world, collects the communication status of each node, ensures that the user's request is not allocated to the unavailable CDN node, and actually does global load balancing through DNS.
Each CDN node consists of two parts: a load-balancing device and a cache server

Load Balancing equipment is responsible for the load balance of each cache in each node to ensure the efficiency of the node, meanwhile, the load balancing device is also responsible for collecting the information of the node and the surrounding environment, maintaining the communication with the global load DNS, and achieving the load balance of the whole system.