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What is a CDN? Thorough explanation of the mechanism and introduction method of CDN!


A CDN is a network for efficient and speedy distribution of digital content. In the 1990s, it was advocated by Akamai, a major American network operator, and the CDN system expanded.
If you are involved in website creation and operation, you will often hear the word “CDN”. I think many people have heard it somehow but haven’t cared about the meaning.
In this article, we will explain how CDNs work, their advantages and disadvantages, and how to use them.


table of contents

  • 1. What is a CDN?
  • 2. How does the CDN work?
  • 3. Benefits of using a CDN
  • 4. Disadvantages of using a CDN
  • 5. How can I use a CDN?
  • 6. Leverage CDNs to improve your website

What is a CDN?

CDN is an abbreviation of “Content Delivery Network”, which is a network that can efficiently and quickly deliver a large amount of digital content to users. The underlying technology and mechanism is a major network in the United States. Proposed by the operator Akamai Technologies in the 1990s.

Conventionally, when a large amount of content (video, image, music, game, etc.) is published on a website, the webserver goes down when visitors are concentrated, or the network is overloaded and displayed. There was a problem that it became slow. To solve these problems, CDNs are now able to mass-deliver large volumes of digital content and deliver them at high speeds using CDNs.


● Background of increasing demand for CDNs

With the spread of the Internet since the 1990s, the content of simple, small-volume websites based on the text has changed to large-capacity content including images, videos, and music.

For example, on e-commerce sites, images and videos are being used more and more so that the appeal of products reaches users. Furthermore, on sale and the release date of popular products, there are times when the number of accesses increases and server downs often occur. As a mechanism to avoid user congestion due to access concentration, the introduction of CDN is emphasized and demand is increasing.

By the way, in recent years, it has come to be called a CDN not only as a network mechanism but also as a billing and authentication system for making profits through mass distribution.


How does a CDN work?

The mechanics of a CDN are very simple. Normally, when delivering digital content, a request is sent to pick up the information needed by the user from the server and return a response. However, if you use a CDN when you make a request, the contents of the previous distribution are stored as a cache (a technology that temporarily stores data such as accessed websites and applications), so you should check with the server originally. You can shorten the flow to be done. This has made it possible to speed up the display of websites.

In addition, because CDN has a network all over the world when a user makes a request, a response from a nearby location is returned.


Benefits of using a CDN

There are many benefits to using a CDN, but it can be especially effective on large websites.


● Page display delay can be reduced

The advantage of using a CDN is that the display speed is improved.

The display speed of the page is affected by the number of simultaneous browser connections. The browser defines the domains that can be connected at the same time, and if it exceeds the default simultaneous connection, it will not be possible to connect and a waiting time will occur. In most basic browsers, the number of simultaneous connections is set to 6. Therefore, if you download 7 or more HTML, CSS, image files, etc. at the same time, a waiting time will occur.

However, if you use a CDN, images and video files are stored on the cache server, so you can download them from a domain different from the origin server. In other words, you can download more than 6 simultaneous connections at once, and as a result, you can reduce the display delay of page speed.


● The load on the server can be reduced

By using a CDN, you can reduce the load on the server.

The server may be overloaded as a cause of slow page speed. When the connection is concentrated on the origin server and the load is applied, the page may not be displayed or an error may occur, which stresses the user. Therefore, by using a CDN, the cache server closer to the user will respond instead, so the load on the origin server can be reduced.


● Reduce server costs

One option is to use a CDN to keep server costs down.

If you are using a rental server, it is common to have a fixed monthly or daily transfer capacity. For websites that use a lot of content such as high-quality images and videos, the transfer capacity becomes a bottleneck, and it is often the case that the server is rented at a high cost.

Therefore, by using a CDN, it is possible to reduce the support on the origin server-side, which makes it possible to reduce server costs. There are costs associated with using a CDN, but it is often relatively cheap compared to the operating costs of the origin server.


Disadvantages of using a CDN

Let’s also check the disadvantages of using a CDN.


● The cache does not reflect the updated information

Since the CDN uses the cache, updating the files on the origin server may not take effect immediately.

For example, when I was using a CDN on an EC site, I accidentally registered the price of the product, and I noticed that and updated the file on the origin server. However, if the cache setting time is set to 3,600 seconds, the modified contents will not be reflected for 1 hour after updating and caching.

If you mistakenly set the amount significantly cheaper, even if it sells well, it will only be a loss. On the other hand, if you set it to a high setting, it will be disadvantageous to the user. Therefore, you need to adjust the cache time if necessary so that it is reflected.


● Cash accidents may occur

Incorrect selection of content and files to be cached may lead to serious accidents such as leakage of personal information and confidential information.

For example, in the case of a website that requires membership registration, if the page containing personal information is cached, it may be delivered to a completely different person. This is called a “cash accident”. Although you can achieve high-speed display using a CDN, it should not be an information leak, so if you always set a cache, do not set it for personal information or important pages.


● Access log may not be obtained

Normally, when a user visits a website, the source information is recorded on the origin server as a log. However, by using a CDN, the access source information remains only on the cache server-side, so it may not be possible to identify it properly. Recently, some CDN services can keep access logs. If access logs are required for website operation, we recommend using a CDN service that can obtain access logs.


How can I use a CDN?

There are two patterns for using a CDN: “a method of deciding from the CDN service business” and “a method of deciding from a rental server”.

Typical CDN service providers include:


● How to decide from a CDN service provider

  • Akamai
  • Amazon CloudFront
  • Cloudflare
  • CDNetworks
  • Fastly



Akamai is a leading American network operator and CDN scourer. It is said that Akamai’s CDN handles 30% of the world’s Internet traffic. It is especially recommended for large-scale sites that have more than 240,000 servers in 130 countries around the world and are accessed from all over the world.


Amazon CloudFront

Amazon CloudFront is a CDN provided by AWS, a major cloud service. In recent years, it has become one of the hottest CDNs used by various companies. Even in Japan, many companies use AWS, and it is becoming indispensable for the development of Internet infrastructure.

If you are using AWS, Amazon CloudFront is also a part of the function, so you do not need to contract separately and it has the advantage that it is easy to link with other services.



Cloudflare is an American company that provides CDNs and security services. We offer free plans and CDN services for individuals as well as for businesses. Cloudflare also operates more than 180 data centers in 80 countries around the world. You can install a CDN for free, so it is recommended for those who want to try it.



CDNetworks is a CDN service with distribution bases mainly in Asia. A network-related company founded in South Korea in 2000, we are expanding into Asia. As it is touted as one of the largest CDN services in Asia, we can respond firmly even in countries such as China and Russia where the distribution of websites is not good. In addition to the CDN service, it is also characterized by being able to consistently implement security measures.



Fastly is a cloud computing service provider founded in 2011 in the United States. Fastly distributes CDNs by pasting the high-performance HTTP accelerator “Varnish” and the webserver “H2O”. Therefore, it has features such as high customizability, high-speed response, and high-speed cache clearing. Dynamic content caching, which was difficult with conventional CDNs, can be easily cached, and real-time analysis and failure detection are possible.


● How to decide from the rental server

  • Sakura rental server
  • X server
  • SEEDS Hosting Service


Sakura rental server

A CDN service is provided by Sakura Internet Inc., which provides a function called “content boost”. There are “Light Plan” and “Standard Plan” depending on the monthly transfer capacity. In both cases, the monthly transfer capacity is up to 100GB and costs 1,100 yen (tax included). The content boost function provided by Sakura Internet can be used with simple operations, so even people without skills or knowledge can easily use it.


X server

This is a CDN service provided by X server Co., Ltd. It is a function to speed up and stabilize a website, and is called “X Accelerator”. The price is free for anyone using the target service of the X server because it is a standard function.

The following versions are available, so select the version you need according to the genre, scale, etc. of the website you are operating.

  • X Accelerator Ver.1: Accelerator of static files
  • X Accelerator Ver.1: Accelerator of static files + Accelerator of PHP programs

“X Accelerator” is recommended for those who are using X server and want to use CDN.


SEEDS Hosting Service

It is a CDN service provided by a corporate hosting service company called Seeds Hosting Service.

Optimal distribution is possible because there are distribution bases in Japan and overseas. Prices vary by delivery area and pay-as-you-go. For example, if the distribution area is up to 100TB in Japan, you will be charged a pay-as-you-go rate of 9 yen per 1GB. In addition to that, a monthly management fee of 5,000 yen is required.


Improve your website with a CDN

With the spread of the Internet, we are now in an era where you can easily enjoy Web content from various devices. Under such circumstances, slowing down the display speed of websites can have a significant impact on sales and closing rates. Therefore, it is important to improve the display speed by utilizing the CDN and cache.

If you ever want to know about similar things, check out the Facebook page Maga Techs



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