A diagram illustrates the CDN network principles, and a diagram shows the cdn principles.

A diagram illustrates the CDN network principles, and a diagram shows the cdn principles.
What?

CDN stands for Content Delivery Network (CDN. The basic idea is to avoid bottlenecks and links on the Internet that may affect data transmission speed and stability, so that content transmission can be faster and more stable. A layer of smart virtual network formed by placing node servers in various parts of the network on the basis of the existing Internet, the CDN system can redirect users' requests to the nearest service node in real time based on the network traffic and connection, load status, distance to the user and response time of each node.. The aim is to allow users to obtain the desired content nearby, solve the problem of Internet congestion, and improve the response speed when users access the website.

 

CDN is a content delivery network built on top of the network. It relies on edge servers deployed in various regions and uses function modules such as server Load balancer, content delivery, and scheduling on the central platform, allows users to obtain the desired content nearby to reduce network congestion and improve user access response speed and hit rate. Key CDN technologies include content storage and distribution technologies. How? The basic principle of CDN is that various cache servers are widely used to distribute these cache servers to areas or networks in which users access the website in a concentrated manner, global load technology is used to direct user access to the nearest normal Cache Server, and the cache server directly responds to user requests. Content Delivery Network (CDN) is a new network construction method. It is a network covering layer that is particularly optimized for publishing broadband rich media on traditional IP networks. In a broad sense, CDN represents a quality and order-based network service model. To put it simply, content delivery network (CDN) is an overall system that has been strategically deployed, including four requirements: distributed storage, Server Load balancer, network request redirection, and content management, content Management and global network Traffic Management are the core of CDN. Based on users' proximity and server load judgment, CDN ensures that the content provides services for users' requests in an extremely efficient manner. In general, content service is based on the cache server, also known as the proxy cache (Surrogate). It is located on the edge of the network and is only one Hop away from the user. At the same time, the proxy cache is a transparent image of the content provider source server (usually located in the data center of the CDN service provider. This architecture enables CDN service providers to provide end users with the best possible experience on behalf of their customers, that is, content providers. These users cannot tolerate any latency in request response time.

1. the user enters the domain name www.web.com into the browser. When the browser finds that there is no dns Cache locally for the first time, it requests to the DNS server of the website;

2. the DNS domain name parser of the website sets the CNAME to point to www.web.51cdn.com, And the request points to the intelligent DNS Server Load balancer System in the CDN network;

3. The intelligent DNS Server Load balancer system resolves the domain name and returns the IP node with the fastest response speed to the user;

4. the user sends a request to the IP node (CDN server;

5. Because this is the first access, the CDN server will request to the original web site and cache the content;

6. Send the request result to the user.

The CDN network adds a Cache layer between the user and the server. How to direct users' requests to the Cache to obtain data from the source server is mainly achieved 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 2: Content elimination mechanism (based on TTL. But the principle is roughly the same.

When a user accesses a website that joins the CDN service, the domain name resolution request is finally sent to the global Server Load balancer DNS for processing. Global Load Balancing DNS provides the Node Address closest to the user through a set of predefined policies, so that the user can get quick services. At the same time, it maintains communication with all CDNC nodes distributed around the world, collects the communication status of each node, and ensures that user requests are not distributed to unavailable CDN nodes, in fact, global load balancing is implemented through DNS.

For Internet users, each CDN node is equivalent to a WEB node placed around it. Through Global Server Load balancer DNS control, users' requests are transparently directed to the nearest node. The CDN server in the node will respond to users' requests like the original server of the website. Because it is closer to the user, the response time must be faster.

Why?

Each CDN node consists of two parts: the Server Load balancer device and the high-speed cache server.

The server Load balancer device is responsible for load balancing of each Cache in each node to ensure node efficiency. At the same time, the Server Load balancer device is also responsible for collecting information about nodes and the surrounding environment, maintain communication with global load DNS to achieve Load Balancing for the entire system. The CDN management system ensures the normal operation of the entire system. It not only monitors all subsystems and devices in the system in real time, generates corresponding alarms for various faults, but also monitors the total traffic in the system and the traffic of each node in real time, and stored in the system database, so that the network administrator can easily perform further analysis. With a complete network management system, you can modify system configurations.

Theoretically, the simplest CDN network has a DNS responsible for global load balancing and a Cache for each node to run. DNS supports resolution of different IP addresses based on users' source IP addresses for nearby access. To ensure high availability, You need to monitor the traffic and health status of each node. When the number of individual caches on a node is insufficient, multiple caches are required. When multiple caches work at the same time, a server Load balancer is required to enable the Cache group to work collaboratively.