CDN setup and product introduction

1. What is a CDN?

The full name of CDN is Content Delivery Network, that is, content distribution network. Its purpose is to publish the content of the website to the "edge" of the network closest to the user by adding a new layer of network architecture to the existing Internet, so that users can obtain the required content nearby and improve the response speed of users visiting the website . CDN is different from mirroring because it is smarter than mirroring, or you can make a metaphor like this: CDN=smarter mirroring+caching+traffic diversion. Therefore, CDN can significantly improve the efficiency of information flow in the Internet network. Technically, it fully solves the problems of small network bandwidth, large number of user visits, and uneven distribution of outlets, and improves the response speed of users' access to the website.

To better understand CDN, let's take a look at the workflow of CDN. When a user visits a website that has joined the CDN service, first determine the best CDN node closest to the user through DNS redirection technology, and at the same time direct the user's request to this node. When the user's request arrives at the specified node, the CDN server (cache on the node) is responsible for providing the content requested by the user to the user. The specific process is: the user enters the domain name of the website to be visited in his browser, the browser requests the local DNS to resolve the domain name, the local DNS sends the request to the main DNS of the website, and the main DNS is determined according to a series of policies The most appropriate CDN node at that time, and send the analysis result (IP address) to the user, and the user requests the content of the corresponding website from the given CDN node.

2. Related technologies of CDN

The implementation of CDN needs to rely on the support of various network technologies, among which load balancing technology, dynamic content distribution and replication technology, and caching technology are the main ones. Let us briefly look at these technologies below.

load balancing technology

Load balancing technology is not only used in CDN, but also in many fields of the network, such as server load balancing and network traffic load balancing. As the name implies, load balancing in the network is to distribute network traffic as evenly as possible to several servers or network nodes that can complete the same task, thereby avoiding overloading of some network nodes. This can not only improve network traffic, but also improve the overall performance of the network. In CDN, load balancing is divided into server load balancing and server overall load balancing (some are also called server global load balancing). Server load balancing refers to the ability to allocate tasks among servers with different performances, which not only ensures that servers with poor performance do not become the bottleneck of the system, but also ensures that the resources of servers with high performance are fully utilized. Server-wide load balancing allows web 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 protect against failures caused by local or regional network outages, power outages, or natural disasters. In the CDN solution, the overall server load balancing will play an important role, and its performance will directly affect the performance of the entire CDN.

Dynamic Content Distribution and Replication Technology

Everyone knows that the response speed of website access depends on many factors, such as whether there is a bottleneck in the bandwidth of the network, whether there is congestion and delay in the route during transmission, the processing capacity of the website server and the access distance, etc. In most cases, the website response speed is closely related to the distance between the visitor and the website server. If the distance between the visitor and the website is too far, the communication between them also needs to go through heavy routing, forwarding and processing, and network delays are inevitable. An effective method is to use content distribution and replication technology to distribute and replicate most of the static web pages, images, and streaming media data that account for the main body of the website to acceleration nodes in various places. Therefore, dynamic content distribution and replication technology is also a major technology required by CDN.

caching technology

Caching technology is not a new technology. Web caching services improve user response time in several ways, such as proxy caching services, transparent proxy caching services, transparent proxy caching services using redirection services, etc. Through the Web cache service, users can minimize the traffic of the WAN when accessing web pages. For corporate intranet users, this means caching content locally without retrieving web pages across a dedicated WAN. For Internet users, this means storing content in their ISP's cache without retrieving web pages over the Internet. This will undoubtedly increase the user's access speed. The core function of CDN is to improve the access speed of the network, so caching technology will be another main technology adopted by CDN.

3. Who needs a CDN?

Since the core function of CDN is to increase the access speed of the network, its users are websites with a large number of visits, such as ICP, ISP, large enterprises, e-commerce websites and government websites. Using CDN technology, these websites do not need to invest in expensive various servers and set up sub-sites. By adopting the CDN, the CDN will be responsible for the information transmission to ensure the normal transmission of the information, and the technicians only need to maintain the content of the website without considering the flow problem. In this way, the website can ensure that users get more new services, can quickly access content on the network, and obtain better service quality. For example, for a website with a relatively large number of visits and a relatively long update period for the accessed content, such as a government website, users often perform a large number of inquiries. Such websites are more suitable for CDN. Also, have you noticed that in the so-called broadband community, the bottleneck is the community's external export. In this way, if the CDN is used, it will undoubtedly provide a guarantee for community users to use broadband applications such as video on demand and online education.

4. Shortcomings of CDN

Any new thing, while bringing improvements to the existing model, must also have certain limitations, and the same is true for CDN. According to Guo Guangzhong, the technical manager of Intercom Network Co., Ltd., poor real-time performance is the fatal flaw of CDN. As the demand for CDNs gradually heats up, this shortcoming will be improved to keep web content pages from remote servers in sync with those in replica servers or caches. The solution is to directly transmit new web content from the server to the cache when the web content changes, or copy the web content of the data source server to the cache server as real-time as possible when the access to web content increases.

5. CDN products

At present, there are Cisco, F5, and Intercom companies that have launched relatively mature CDN products. The CDN of the former two is based on hardware systems, while the CDN of the latter is a general-purpose platform based on software. Line and service advantages. Let's briefly analyze the interconnected CDN - Smart CDN.

Interconnect adopts the combination of overall load balancing (GSLB), caching technology (Cache) and mirror technology (Mirror) to provide customers with off-site network acceleration services. The specific solution is to use Intercom's network acceleration service in cities and regions where users are concentrated outside the main site of the website. Intercom's intelligent GSLB system guides website users to access the "best" Cache/Mirror server through the Intercom private network, thereby bypassing the Internet Congested links, reduce the load on the main site server, realize remote network acceleration, and solve the problems that cannot be solved by simple Cache/Mirror.

Smart CDN works through DNS resolution or HTTP redirection, and completes the transmission and synchronization of content through the Cache server or remote mirror sites. The accuracy rate of user location judgment by DNS method is greater than 85%, and the accuracy rate of HTTP method is more than 99%. According to actual calculations, the ratio of the amount of inflowing data from user access in each cache server group to the amount of data fetched from the cache server to the original website is between 2:1 and 3:1, that is, 50% to 70% of the duplicate data to the original website is shared. The amount of access data (mainly pictures, streaming media files, etc.). For mirroring, except for data synchronization traffic, the rest are completed locally without accessing the original server.

The Smart CDN system judges the user's location based on the IP address actually accessed by the user, and directly directs the user's access to the site with the fastest response. The entire system is easy to manage. Users can determine which content needs to be distributed through the GUI, and the system will automatically complete the entire process of content copying, updating, and database synchronization. Moreover, the system has the ability of self-diagnosis and load balancing, and any link failure will not affect the accessibility of the entire system.

It can be said that the load balancing technology plays an important role in the CDN, and its capacity has a direct impact on the performance of the CDN. The load balancing adopted by Smart CDN has certain advantages, which are mainly reflected in the following aspects.

1. High intelligence

Using virtual IP (VIP) addresses to represent target servers and applications, Smart CDN assigns sessions to the highest available servers and monitors each session throughout. Automatically re-registers after service is restored, and provides full address translation when forwarding client and server packets. Smart CDN adopts a variety of different load balancing methods including round-robin method, least connection method, hash method or least error method, and configures the maximum connection number threshold and weighted value for individual servers, which can effectively avoid server overload.

2. high reliability

The Smart CDN architecture is based on a high-speed backbone network dedicated to interconnection. This backbone network provides network connectivity with minimal delay, thereby ensuring the normal function and high performance of GSLB, which is better than GSLB based on the public network. Moreover, when the Internet exit of the computer room at the main site fails, Smart CDN can also automatically and transparently guide users from other sub-site Internet entrances to the main site server, thereby improving network reliability.

3. high availability

The hot backup method is used to detect and fail over server links, switching ports and switches in a very short time, so that applications are not affected by failures. Once any server or server group fails or is blocked, users will be automatically directed to the next best backup server or site, thereby further improving the availability of services and content.

4. high redundancy

Smart CDN runs on the interconnected "three-ring nested" network backbone architecture, which has high redundancy characteristics, thus ensuring high reliability and high availability, which is very different from other public network-based GSLB solutions.

In addition, the advantages of Smart CDN in terms of services are reflected in: through the interconnection of the dedicated link system, the response speed of user access can be improved; the content synchronization of multiple servers in the three regions of the Taiwan Strait is guaranteed; the peak load (peak load) is eliminated. ) pressure on export links and server performance; increased bandwidth utilization of leased links; reduced load on original Web/FTP sites, etc.