Understand CDN

Definition : cdn(Content Delivery Network) Content based distributed distribution network .

What is? cdn Service? , Simply speaking , It is to let the original access to the traffic or browser of the master server , Go to the cache server deployed near him to handle , such , It can greatly reduce the pressure on the main server , And at the same time, it can improve the access speed of users , Reduce the pressure of bandwidth .

Generally need cdn The service website will choose the organization scheme :

Through rented IDC Provide additional CDN service ;

2.. Buy professional CDN Service provider's service ;

3. Set up your own CDN The Internet ; The cost increases in turn .

Cdn The purpose of design is to realize web Load balancing of content , Prevent access request hotspots , Delayed response , , etc. , It can also be used in game architecture , Improve the speed of game access and pull resources .

Cdn Characteristics :

1, Distributed storage ,2, Through intelligent dns Parse or http Redirection realizes load balancing of content distribution ,3, Global load balancing management and content management ,

Cdn The composition of :

cdn The functional entities included in the network include content caching devices , Content router ,cdn Content management system, etc ,

Content caching ： by CDN Network nodes , At the user access point , It's a content delivery device for end users , Cacheable static WEB Content and streaming content , Realize the edge propagation and storage of content , So that users can visit nearby .

Content switch :  At the user access point , It can balance the load of a single point of view content caching device , And load balancing access control for content .

The content router is responsible for scheduling users' requests to the appropriate devices , Dynamically balance the load distribution of each content cache site , Choose the best access site for the user's request , At the same time to improve the usability of the website , Content routers can make routes based on many factors , Including the proximity between the site and users 、 Availability of content 、 Network load 、 Equipment condition, etc .

Be careful : Load balancing is the whole cdn At the heart of , The accuracy and efficiency of load balancing will directly determine the whole cdn The efficiency of .

Cdn cache :  cdn Cache is a register that temporarily stores network signals , stay cdn This large number of network request signals will be cached in the database , then cdn The database will be based on the current status of the network server , Allocate different network request signals , This will enable many idle network servers to work ,.

Cdn Network structure :

Cdn The network is generally divided into central and edge nodes , The center is responsible for overall load balancing management and content management ..

Architecture diagram :

 

here cdn Divide the levels : stay cdn In the system , Responsible for providing content services to users cache Devices are deployed throughout cdn The Internet I edge , So it becomes an edge node .

Cdn The central layer of is responsible for the overall management and control , At the same time, it saves the most cache, When the edge layer misses , The central layer will be requested , If the central layer also misses, request data from the source . If the origin station returns to the central layer , Or the central layer itself has corresponding data returned to the edge layer , The edge will be returned to the user and a cache will be made locally .

If the system is relatively large , The edge layer requests too much content from the center , You need area nodes , Acting as agent , Responsible for the management and control of an area .

CDN How it works

Cdn The network adds a layer between users and servers cache, How to guide the user's request to cache On , Then we need to use dns, adopt dns The parsing adjustment of the request is a forwarding .

General process : 1, The user requests a domain name , 2, The browser resolves the domain name , Here's the details dns The parsing process is not elaborated , because cnd The domain name resolution process has been adjusted , Through the function analysis library, we get the corresponding cname Record the domain name after , So the browser will be right again cname Domain name to access , request ip, In the process , Use the global load balancing strategy dns analysis , Among them, according to the geographical location and other information, it is analyzed to the nearest location , Let users access it .

3, Get cached server ip Address , The browser initiates an access request ,

4, The cache server passes on request cache Internal dedicated dns After the parsing , Get the authenticity of the domain name ip, Then send a request to the real server , Request the corresponding data ,

5, The origin server sends response data , After the cache server gets the data , Cache a backup locally , Then return a copy to the user , Complete the process .

Content distribution technology :

 

When the source site needs to distribute content , You can distribute the distribution to CDN Intermediate source Again by CDN The intermediate source forwards the content to each CDN node If CDN The node needs to request a URL When content is requested , The request will be sent to CDN Intermediate source Again by CDN The intermediate source actively sends the request content to the source station , Finally, the acquired data is stored on the intermediate source and content node , So as to achieve the effect of node acceleration .

There are mainly two ways , Take the initiative to push : The origin server pushes the latest data to each node , updated .

Passive push : Passive access is when users visit , Send a request to the mirror server , If there is content on the mirror server , Just go back to the user , without , Get it from the server source station and return it to the user .

meanwhile cdn The content on the edge node is not updated in real time , Files are stored as key value pairs , Key value pairs key Usually file url, Value saves the location of the file in the server , Or binary value of the file , At the same time, the file is saved http Header information .