Shulou(Shulou.com)06/03 Report--

Compared with other CDN service providers, the main advantages of CDN include stable and fast, cost-effective, easy to use, efficient and intelligent. More users will ask about the advantage of stability and speed. Generally speaking, CDN is characterized by sharing the pressure on the origin server, avoiding network congestion, accelerating the distribution of website content in different regions and different scenarios, and improving the speed of resource access. The following is to introduce the principle and process analysis of CDN acceleration service.

1. The user enters the domain name www.web.com into the browser, and the browser finds that there is no dns cache locally for the first time, and then requests the DNS server of the website.

two。 The DNS domain name parser of the website sets CNAME, points to www.web.51cdn.com, and the request points to the intelligent DNS load balancing system in the CDN network.

3. The intelligent DNS load balancing system parses the domain name and returns the IP node with the fastest response to the user.

4. The user makes a request to the IP node (CDN server)

5. Since this is the first visit, the CDN server requests the original web site and caches the content

6. The result of the request is sent to the user.

CDN network is to add a Cache layer between the user and the server, how to direct the user's request to the Cache to get the data of the source server, mainly by taking over DNS, this is the most basic principle of CDN, of course, many details are not involved, such as step 1, first request to the local DNS server. Step 5, content elimination mechanism (according to TTL), etc. But that's pretty much how it works.

When a user visits a website that joins the CDN service, the domain name resolution request will eventually be handed over to the global load balancer DNS for processing. The global load balancer DNS provides users with the node address closest to the user at that time through a set of pre-defined policies, so that users can 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 user requests are not allocated to unavailable CDN nodes, and actually does global load balancing through DNS.

For the average Internet user, each CDN node is equivalent to a WEB placed around it. Through the control of the global load balancer DNS, the user's request is transparently directed to the nearest node, and the CDN server in the node will respond to the user's request just like the original server of the website. Because it is closer to the user, the response time must be faster.

Each CDN node consists of two parts: a load balancing device and a cache server

The load balancing device is responsible for the load balancing of each Cache in each node to ensure the work efficiency of the node; at the same time, the load balancing device is also responsible for collecting the information between the node and the surrounding environment, maintaining communication with the global load DNS, and realizing the load balancing of the whole system. The management system of CDN is the guarantee of the normal operation of the whole system. It can not only monitor each subsystem and equipment in the system in real time, and generate corresponding alarm to all kinds of faults, but also monitor the total flow in the system and the flow of each node in real time, and save it in the database of the system. so that network managers can easily carry out further analysis. Through the perfect network management system, users can modify the system configuration.

In theory, the simplest CDN network can run with a DNS responsible for global load balancing and a Cache for each node. DNS supports parsing different IP according to the user's source IP address to achieve nearest access. In order to ensure high availability, it is necessary to monitor the traffic and health status of each node. When the number of a single Cache of a node is not enough, multiple Cache and multiple Cache are needed to work at the same time, and load balancer is needed to make the Cache group work together.

If there is anything else you don't understand, you can find our CDN technical engineer on the official website. CDN technical engineer has more than ten years of experience in the industry, so it will be more detailed and professional than the editor's answer. Official website link www.yisu.com

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