Let’s talk about what CDN is. Do you know these characteristics?

Preface

When we browse the web, watch videos, and download files every day, there is a technology hidden in the background that is silently providing services for us. It is CDN (Content Delivery Network).

CDN technology has become an indispensable part of today's Internet architecture. Its existence has greatly improved the speed and experience of accessing network content.

So, do you really understand what CDN is? Let’s take a deeper look.

What is a CDN?

CDN is the abbreviation of Content Delivery Network, which is a network architecture that provides efficient and fast content transmission and distribution services by deploying server nodes around the world.

How does CDN work?

The working principle of CDN is to cache content (such as web pages, pictures, videos, etc.) on the server node closest to the user. When the user requests to access these contents, CDN will automatically select the nearest server node to provide the content based on the user's geographical location and network conditions, thereby achieving fast content transmission and distribution.

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Content Caching

CDN caches the static content of the website (such as images, CSS, JavaScript, etc.) to the server nodes closest to the user. These nodes are usually located in data centers around the world, covering a wide range.

Routing

When a user requests to access a website, CDN will select the server node closest to the user to provide content based on the user's geographical location and network conditions. This selection process is usually completed through DNS resolution.

Content Delivery

Once the CDN determines the best server node, it forwards the request to that node and retrieves the cached content from that node. This can reduce network latency and increase content delivery speed.

Dynamic content processing

For dynamic content (such as personalized pages, user login information, etc.), CDN will forward the request to the source server, and then cache the response content on the server node so that it can be directly obtained from the node the next time it is requested.

Cache Updates

When the content on the source server changes, the CDN will update the cache in time to ensure that users get the latest content. This can be achieved by regularly checking the content changes on the source server or by the source server actively notifying the CDN.

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Through the above workflow, CDN can provide fast and reliable content transmission and distribution services, improving website access speed and user experience.

At the same time, CDN can also improve the availability and stability of the website through technologies such as load balancing and failover.

advantage

Improve access speed

Since CDN server nodes are distributed all over the world, users can obtain content from the node closest to them, reducing network latency and increasing access speed.

Reduce the load on the origin server

CDN can cache and distribute static content, reducing the load pressure on the source server and improving the stability and reliability of the website.

Provide high availability

CDN provides high-availability services through redundant deployment of multiple server nodes. Even if a node fails, other nodes can still provide content.

Save bandwidth costs

CDN can reduce bandwidth consumption for data transmission through caching and compression technology, thereby reducing bandwidth costs.

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CDN is widely used in websites, mobile applications, live video, online games and other fields, and can provide better user experience and service quality.

What is back-to-source?

Back-to-origin means that when the cached content on the CDN node expires or does not exist, the CDN will request the latest content from the source server and cache it on the node so that it can be directly obtained from the node the next time the user requests it.

1. When a user requests to access a certain content, CDN will first check whether there is a cache of the content on the node. If there is a cache and it has not expired, CDN will directly return the cached content from the node to improve access speed. However, if there is no cache on the node or the cache has expired, CDN needs to initiate a back-to-source request to the source server.

2. The back-to-origin request forwards the user's request to the origin server, which generates a response based on the content of the request and returns the response to the CDN. The CDN caches the content returned by the origin server on the node and returns it to the user. At the same time, the CDN also updates the expiration time of the cache so that it can be directly obtained from the node the next time it is requested.

3. The frequency of back-to-source requests depends on the expiration time of the cache and the frequency of content updates. If the cache expiration time is long or the content is updated less frequently, the frequency of back-to-source requests will be low. However, if the cache expiration time is short or the content is updated more frequently, the frequency of back-to-source requests will be high.

4. The process of returning to the source will increase the latency of the request because the request needs to be forwarded to the source server and wait for the response. However, returning to the source can ensure that users get the latest content, especially for dynamic content or frequently updated content. At the same time, CDN can also reduce the latency and bandwidth consumption of return-to-source requests through some optimization strategies, such as incremental return to the source and intelligent return to the source.

How to determine whether back-to-origin occurs?

View the logs of the CDN node

The CDN node will record detailed information for each request, including whether the cache is hit, whether a back-to-origin request has occurred, etc. By viewing the node log, you can see whether there is a record of a back-to-origin request.

Monitor the cache hit rate of CDN nodes

The cache hit rate of a CDN node indicates how many requests can obtain content from the node's cache without going back to the source. If the cache hit rate is low, it means that more requests need to go back to the source.

Monitor the number of requests to the origin server

The back-to-origin request forwards the user's request to the origin server, so you can determine whether a back-to-origin request has occurred by monitoring the number of requests to the origin server. If the number of requests to the origin server is high, it means that there are more requests that need to be back-to-origin.

Monitor the traffic of CDN nodes

Back-to-origin requests increase the traffic consumption of CDN nodes, so you can monitor the traffic of the node to determine whether back-to-origin has occurred. If the traffic of the node is high, it means that there are more requests that need to be back-to-origin.

Is using CDN definitely faster than not using it?

Not necessarily. Using a CDN can improve the access speed and performance of a website or application, but it is not guaranteed to be faster than not using a CDN in all cases.

The main function of CDN is to increase access speed by caching content on nodes closer to users, reducing the transmission distance and network latency of requests. For static content or content that rarely changes, the effect of CDN is usually very significant, because such content can be cached on CDN nodes, and users can obtain it directly from the nodes without going back to the source.

However, for dynamic content or frequently changing content, the effect of CDN may be limited. Because such content cannot be cached on CDN nodes, each request needs to go back to the source to obtain the latest content, which increases the latency of the request.

In addition, it takes a certain amount of time to update the cache of CDN nodes. If the content is updated frequently, users may not be able to obtain the latest content immediately.

In addition, CDN performance is also affected by other factors, such as the network quality of the CDN provider, the distribution of nodes, the performance of the source server, etc. Different CDN providers and configuration methods may have different performance.

Therefore, when choosing whether to use CDN, you need to consider factors such as the characteristics of the website or application, the nature of the content, the geographical distribution of users, and conduct actual testing and evaluation to determine whether faster access speeds can be achieved.