What is CDN and CDN Acceleration Principle

With the development of the Internet, users pay more attention to the browsing speed and effect of the website when they use the network, but because of the increasing number of netizens, the network access path is too long, so that the quality of users ' access is seriously affected. Especially when the link between the user and the website is congested with large traffic data, the poor access quality is an urgent problem to be solved for the area where Internet users are rapidly increasing. How can users everywhere make high-quality access, and minimize the resulting costs and site management pressure. The Content Publishing Network (Delivery Network,cdn) was born. first, what is a CDN.

The full name of the CDN is the Content Delivery network, which is the contents distribution networks. The goal is to increase the responsiveness of users to websites by adding a new layer of network architecture to the existing Internet, publishing the content of the site to the edge of the network closest to the user, so that users can get the content they need nearby. A CDN is different from mirroring because it is smarter than mirroring, or it can be used as a metaphor: cdn= more intelligent mirror + cache + traffic diversion. Therefore, CDN can obviously improve the efficiency of information flow in Internet network. From the technical comprehensive solution due to network bandwidth is small, user access is large, dot distribution is not equal problem, improve the response speed of users to visit the site.

To better understand the CDN, let's look at the workflow of the Cdn. When a user accesses a website that has been added to a CDN service, it first determines the best CDN node that is closest to the user by using DNS redirection technology and points the user's request to that node. When a user's request arrives at the specified node, the CDN server (the cache on the node) is responsible for providing the user with the requested content. The specific process is: the user in their own browser to enter the domain name of the site to visit, the browser to the local DNS request for the domain name resolution, local DNS requests to the site's primary DNS, the primary DNS based on a series of policies to determine the most appropriate CDN node, and the results of the resolution (IP address) sent to the user, The user requests the content of the corresponding site to a given CDN node. second, the relevant technology of CDN

CDN implementation needs to rely on a variety of network technology support, including load balancing technology, dynamic content distribution and replication technology, caching technology is the main number, let's take a brief look at these several technologies.

Load Balancing Technology
Load balancing technology is not only used in CDN, but has been widely used in many areas of the network, such as server load balancing and network traffic load balancing. As the name implies, the load balance in the network is to distribute the network traffic as evenly as possible to several servers or network nodes that can accomplish the same task, thus avoiding the overloading of some network nodes. This can improve the network traffic, but also improve the overall performance of the network. In a CDN, load balancing is divided into server load balancing and server overall load balancing (also known as server Global load balancing). Server load balancing is the ability to assign tasks between servers with different performance, which can ensure that the servers with poor performance are not the bottleneck of the system, and that the resources of high performance servers can be fully utilized. Server-wide load Balancing allows Web network hosts, portals, and businesses to distribute content and services based on geographic location. Improve fault tolerance and availability by using multi-site content and services to prevent failures due to outages, power outages, or natural disasters in local or regional networks. In the CDN scheme, the server overall load balance will play an important role, its performance will directly affect the performance of the whole CDN.

Dynamic content distribution and replication technology
As we all know, the speed of Web site access response depends on many factors, such as whether the bandwidth of the network has bottlenecks, whether the route in transit is blocked and delayed, the processing power and access distance of the Web server. In most cases, the responsiveness of the website and the distance between the visitor and the Web server are closely related. If the distance between the visitor and the website is too far, the communication between them needs to pass through the heavy route forwarding and processing, the network delay inevitably. One effective way is to use content distribution and replication technology to replicate most of the static Web pages, images, and streaming data distributed by the main body of the site to accelerating nodes everywhere. Therefore, dynamic content distribution and replication technology is also a key technology required by CDN.

Caching technology
Caching technology is no longer a fresh technology. The Web caching service improves user response times in several ways, such as the proxy cache service, the transparent proxy cache service, the transparent proxy caching service using the redirection service, and so on. The Web caching service allows users to minimize the WAN traffic when they visit a Web page. For corporate intranet users, this means caching content locally without having to retrieve the page through a dedicated WAN. For Internet users, this means storing content in their ISP's cache without having to retrieve Web pages over the Internet. This will undoubtedly increase the user's access speed. The core role of CDN is to improve the speed of network access, so the caching technology will be another major technology used by CDN. third, who needs CDN.

Since the core role of CDN is to improve the speed of network access, then its users are a large number of sites, such as ICP, ISP, large enterprises, e-commerce sites and government sites. Using CDN Technology, these sites do not need to invest in expensive types of servers and set up sub-sites. Through the adoption of CDN,CDN will be responsible for information transfer work to ensure the normal transmission of information, and technical personnel only need to maintain the content of the site, do not need to consider traffic problems. In this way, the site can ensure that users get more new business, can quickly access the content on the network, to obtain better quality of service. For example, for a large number of visits, and the content of the update period of the site is more long, such as government sites, users often do a lot of query work. This kind of website is more suitable to use CDN. Also, have you noticed that in the so-called broadband community, the bottleneck is the external export of the community. In this way, if the use of CDN undoubtedly to the Community users using video-on-demand, network education and other broadband applications to provide a guarantee. Iv. deficiencies of the CDN

Any new things, in the existing model to bring improvements, but also there must be some limitations, CDN is also the case. Real-time is not very good is the CDN's fatal flaw. As the demand for CDN increases, this flaw will be improved so that the Web content pages from the remote server are kept in sync with the Web pages in the replica server or cache. The workaround is to transfer the new network content directly from the server side to the cache when the network content changes, or to replicate the network content of the data source server to the cache server as real-time as possible when access to the network content increases.

Original link: http://www.cnblogs.com/seanxyh/archive/2013/04/16/3023499.html