What is CDN

I. Working Principle of CDN

The content delivery network (CDN) uses intelligent routing and traffic management technologies to promptly discover the acceleration nodes that provide visitors with the fastest response, and direct visitor requests to the acceleration nodes, provided by the acceleration Node
Content Service. Using the content delivery and replication mechanism, CDN customers do not need to change the original website structure. They only need to modify a small number of DNS configurations to accelerate the network response speed.

When a user accesses a website using the CDN service, the DNS domain name server uses the cname method to request the final Domain Name
Request to redirect to the intelligent DNS load balancing system in the CDN system. The intelligent DNS Server Load balancer system uses a set of pre-defined policies (such as content type, geographical region, and network load status)
It is enough to provide users with the fastest response to the user's node address, so that users can get quick services.

At the same time, it also communicates with all CDN nodes distributed in different locations, collects the health status of each node, and ensures that user requests are not distributed to any unavailable node. However, chinanetcenter CDN also has the capability of adaptive route adjustment in the case of network congestion and failure.

After the CDN service is used, the user's access process is shown in:

Figure CDN user access Flowchart

	The user provides the browser with the domain name to access the website, and the domain name resolution request is sent to the DNS domain name resolution server of the website;
	Because the DNS server of the website sets a cname for the resolution of this domain name, the request is directed to the intelligent DNS Server Load balancer System in the CDN network;
	The intelligent DNS Server Load balancer system intelligently resolves domain names and returns the node IP address with the fastest response speed to users;
	After obtaining the IP address of the fastest node, the browser sends an access request to the CDN node;
	Because this is the first access, the CDN node will return to the origin site to retrieve the data requested by the user and send it to the user;
	When other users access the same content again, CDN will directly return the data to the customer to complete the request/service process.

Through the above analysis, we can see that the CDN service can accelerate Website access while making it transparent to normal users. That is, after the cache is added, the user client does not need to make any settings, enter the original Domain Name of the accelerated website to access the website.

Ii. CDN Introduction

The full name of CDN is content delivery.
Network, that is, the content delivery network. The purpose is to add a new network architecture to the existing Internet to publish website content to the "edge" closest to the user's network, so that users can
In order to obtain the desired content nearby, solve the internet congestion situation, and improve user access to the network
The response speed of the website. Technically, it solves the slow response speed caused by low network bandwidth, large user traffic, and unevenly distributed outlets.
CDN Internet content publishing network (Content Delivery Network)
CDN is an effective method to solve the problem of poor Internet performance.
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. The existing
An Intelligent Virtual Network Based on the internet, the CDN system can re-export users' requests in real time based on the network traffic and the connection, load status, distance to the user and response time of each node.
To the nearest service node to the user.

In fact, 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 generation
This table describes a network service model based on quality and order. To put it simply, content delivery network (CDN) is a strategically deployed overall system, including distributed storage, Server Load balancer, network request redirection, and internal
Content management and global network traffic management (Traffic)
Management) is 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
Based on the cache server, this service is also called the proxy cache (surrogate). It is located on the edge of the network and is only one hop away from the user.
Hop. 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 represent them.
Customers, that is, content providers, provide end users with the best possible experience, and these users cannot tolerate any latency in the request response time. According to statistics, CDN technology can be used to process the entire website page
70% ~ 95% of content access Traffic reduces the load on the server and improves the performance and scalability of the website.

Compared with the existing content publishing mode, CDN emphasizes the importance of the network in content publishing. By introducing active content management and global load balancing, CDN is fundamentally different from traditional content delivery
Deployment mode. In the traditional content publishing mode, content publishing is completed by the ICP application server, while the network only acts as a transparent data transmission channel. This transparency is manifested only in the network quality assurance.
In terms of data packets, service quality cannot be differentiated based on different content objects. In addition, due to the "Best Effort" feature of the IP network, the Quality Assurance relies on the end-to-end provision between users and application servers.
It is fully and far greater than the actual amount of bandwidth required. In this content publishing mode, not only is a large amount of valuable backbone bandwidth occupied, but the load of the ICP application server also becomes very heavy, and
Predictable. In the event of some hot events and surge traffic, local hot spots will be generated, so that the application server will be overloaded and quit the service. Another deficiency in the content publishing mode of this center-based application server
Due to the lack of personalized services and the distortion of the value chain of broadband services, content providers have undertaken content publishing services that they should not do or do badly.

Throughout the value chain of broadband services, content providers and users are located at both ends of the entire value chain, and network service providers are used in the middle to connect them. With the maturity of the Internet industry and the transformation of business models
More and more roles in the value chain are also subdivided. Such as content/Application operators, managed service providers, backbone network service providers, and access service providers. Every role in this value chain
Division of labor and cooperation are required to perform their respective duties in order to provide good services to the customer, resulting in a win-win situation. In terms of the combination of content and network, content publishing has gone through the content (Application) server and
IDC. The IDC boom also gave birth to the role of hosting service providers. However, IDC cannot solve the issue of effective content publishing. The content in the center of the network does not address the proportion of backbone bandwidth
And establish the traffic order on the IP network. Therefore, pushing content to the edge of the network to provide nearby edge services for users, so as to ensure the quality of service and the access order on the entire network becomes an obvious
Select. This is the CDN service mode. The establishment of CDN solves the dilemma of "centralization and decentralization" for content operators, which is undoubtedly valuable for building a good Internet value chain.
Value is also an indispensable optimal website acceleration service.

Currently, large websites with high access volume in China, such as Sina and Netease, all use the CDN network acceleration technology. Although the Website access is huge, it will feel fast wherever it is accessed. Generally, if the website server is in China Netcom, the access by telecom users is very slow. If the server is in China Telecom, the access by Netcom users is very slow.

It adopts a distributed network cache structure (that is, the internationally popular Web
By adding a new network architecture to the existing Internet, the website content is published to the Cache Server closest to the user.
To determine the content that the user needs to access the cache server from the nearest node, to solve the Internet network congestion and improve the response speed of the user's Website access, as if multiple
Accelerator for fast and redundant acceleration of multiple websites.

Iii. CDN features

1. Local cache acceleration improves the access speed of Enterprise websites (especially websites containing large numbers of images and static pages) and greatly improves the stability of these websites.

2. The image service eliminates the bottleneck of interconnection between different carriers, achieves network acceleration across carriers, and ensures good access quality for users in different networks.

3. Remote acceleration Remote Access Users can automatically select the Cache Server Based on DNS load balancing technology and select the fastest cache server to accelerate remote access.

4. Bandwidth Optimization automatically generates a remote mirror (image) cache server for the server. Data is read from the cache server during remote user access, reduces remote access bandwidth, network traffic, and web server load of the original site.

5. the widely distributed cluster anti-attack CDN nodes and intelligent redundancy between nodes can effectively prevent hacker intrusion and reduce various types of D. d. o. s attack impact on the website, while ensuring good service quality.