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2025-01-18 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Network Security >
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Before describing the implementation principle of CDN, let's first look at the access process of traditional non-cached services to understand the difference between CDN cache access mode and non-cached access mode:
The process for users to visit websites that do not use CDN caching is:
1)The user provides the domain name to the browser to access;
2)The browser calls the domain name resolution function library to resolve the domain name to obtain the IP address corresponding to the domain name;
3)The browser uses the obtained IP address and domain name to send a data access request to the service host.
4)The browser displays the content of the web page according to the data returned by the domain name host.
Through the above four steps, the browser completes the whole process from receiving the domain name that the user wants to access to obtaining data from the domain name service host. CDN network is to add Cache layer between users and servers, how to direct user requests to Cache to obtain data from source servers, mainly by taking over DNS, let's take a look at the process of accessing websites after using CDN cache:
After using CDN cache, the visit process of the website becomes:
1)The user provides the domain name to the browser to access;
2)The browser calls the domain name resolution library to resolve the domain name. Since the CDN adjusts the domain name resolution process, the resolution function library generally obtains the CNAME record corresponding to the domain name. In order to obtain the actual IP address, the browser needs to resolve the obtained CNAME domain name again to obtain the actual IP address. In this process, the global Load Balancer DNS resolution is used, such as resolving the corresponding IP address according to the geographical location information, so that the user can access it nearby.
3)This time, the IP address of the CDN cache server is parsed. After the browser obtains the actual IP address, it sends an access request to the cache server.
4)According to the domain name to be accessed provided by the browser, the cache server obtains the actual IP address of the domain name through the internal dedicated DNS resolution of Cache, and then the cache server submits an access request to the actual IP address;
5)After the cache server obtains the content from the actual IP address, on the one hand, it saves it locally for later use, and on the other hand, it returns the obtained data to the client to complete the data service process.
6)After the client obtains the data returned by the cache server, it displays it and completes the whole browsing data request process.
Through the above analysis, we can get that in order to achieve transparency to ordinary users (that is, after adding cache, the user client does not need to make any settings and can directly access the original domain name of the accelerated website), but also to provide CDN website acceleration services for the specified website while reducing the impact on ICP, as long as the domain name resolution part of the entire access process is modified to achieve transparent acceleration services.
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