CDN service provider and CDN FAQ

1. CDN service provider

1. chinacache, chinanetcenter, Dilian, quicknet, 21 vianet, CDN Alliance

2. The CDN bandwidth and node count of chinacache are the largest, followed by chinanetcenter, duilian, and quickmoney. Dilian is divided by chinanetcenter, and early CDN staff of quickmoney are also related to chinanetcenter. 21 vianet 2008 began to intervene in the CDN market. The common feature of this solution is that large national IDCs have switched to CDN services, and the CDN alliance is gaining momentum. Some fixed nodes should also be deployed one after another. China Telecom and China Netcom have also begun to implement CDN. However, due to system restrictions, it is very troublesome for a local China Telecom Netcom company to distribute data nationwide.

2. Selection of CDN service provider Conditions

1. If your customer base is only concentrated in a small local area, CDN may be of little use to you.

2. First, the first choice is formal, and the second choice is appropriate. For example, if you are a foreign company, you must select a CDN node that has an advantage abroad. Of course, local CDN services are selected in China. Third, looking at nodes doesn't mean that the more CDN nodes, the better. Depending on your needs, select based on market distribution. Of course, it is better across the country.

3. Reliability, stability, response time, hit rate, coverage, cross-network access, controllability, and DNS resolution stability. Recently, I watched a video and found that DNS resolution frequently experienced problems, affecting the user experience.

 

Iii. CDN service cost

1. the billing method is based on traffic, bandwidth, and the third peak value. Generally, the billing method is based on traffic, that is, the amount of money per g.

2. self-built CDN with low initial cost and convenient control. However, as the scale increases, the cost increases and maintenance is difficult.

3. Generally, the access volume to the master server is reduced by 50%-70%.

4. 80% of users generally access 20% of resources, which serves as the basic theoretical support for CDN feasibility.

4. Basic Implementation of CDN.

1. memory cache.

2. reverse proxy for software squid, nginx, Apache, etc. Squid and nginx are implemented in windows.

3. It mainly implements static content caching, and some service providers also support dynamic content caching.

V. CDN Problems and Solutions

1. CDN cache. After a cache is generated, it is difficult to clear the CDN cache if the file is updated. As a result, users cannot access the latest file for a long time. If JavaScript or CSS files are updated, this will cause page clutter and JS execution errors.

Solution: A. You can use the API provided by the CDN vendor to clear the cache, but there is generally a limit on the number of calls within a period of time. You can also design a hook to clear the cache. B. Set JS files with version numbers such as http://test.com/js/test.js? 123456. Some caches in this way will not recognize "?" Subsequent parameter changes lead to a long version of the requested file. Or else. C. http://test.com/CSS/common.css? The time interval 123456.css, such as this structure, is also a miraculous solution. The subsequent time interval 123456.css can be modified as needed. Add the address of the d.css and JS files, for example? V = version 123, which is automatically increased by 1 for each release.

Conclusion: The above is a solution to the CDN cache problem after static files are updated. The simplest solution is to add parameters and different parameters after files, to control the CDN cache. In this way, note that some CDN service providers with 2 levels do not support parameter formats. HookProgramUnreliable, CDN static files are scattered everywhere, and hook triggering is limited. The provided API is relatively reliable, but the implementation is a little complicated and may exist. During the update period, your static file has been updated, but the API execution will be in a hurry in the future, the risk of some errors caused by clearing all the caches, and the number of API executions is limited. For example, when the API executes half of the file update requests, the maximum number of executions has been reached. You cannot clear the cache through APIS.

2. the cache hit rate is too low, which may result in poor CDN performance. Generally, the cache hit rate can reach 90 + % and reach 95% or more.