What is a CDN (Content Delivery Network)?

The primary purpose of a content delivery network (CDN) is to reduce latency, or reduce the delay in communication created by a network's design. Because of the global and complex nature of the internet, communication traffic between websites (servers) and their users (clients) has to move over large physical distances. The communication is also two-way, with requests going from the client to the server and responses coming back.

A CDN improves efficiency by introducing intermediary servers between the client and the website server. These CDN servers manage some of the client-server communications. They decrease web traffic to the web server, reduce bandwidth consumption, and improve the user experience of your applications.

Content delivery network (CDN) technology emerged in the late 1990s with the focus on faster content delivery over the internet:

First generation

First-generation CDN services focused on networking principles of intelligent network traffic management and data centers for replication.

Second generation

Second-generation CDNs arose in response to the rise of audio and video streaming services, especially video on demand and news on demand. The technology also evolved to solve new challenges in content delivery on mobile devices. Companies used cloud computing techniques and peer-to-peer networks to accelerate content delivery.

Third generation

Third-generation CDNs are still evolving. AWS is driving innovation as one of the leading CDN service providers in the world. With most web services centralized in the cloud, the focus is now on edge computing—managing bandwidth consumption using smart devices that communicate intelligently. Autonomous and self-managed edge networks might be the next step in CDN technology.

Content delivery networks (CDNs) work by establishing a point of presence (POP) or a group of CDN edge servers at multiple geographical locations. This geographically distributed network works on the principles of caching, dynamic acceleration, and edge logic computations.

Caching

Caching is the process of storing multiple copies of the same data for faster data access. In computing, the principle of caching applies to all types of memory and storage management. In CDN technology, the term refers to the process of storing static website content on multiple servers in the network. Caching in CDN works as follows:

1. A geographically remote website visitor makes the first request for static web content from your site.
2. The request reaches your web application server or origin server. The origin server sends the response to the remote visitor. At the same time, it also sends a copy of the response to the CDN POP geographically closest to that visitor.
3. The CDN POP server stores the copy as a cached file.
4. The next time this visitor, or any other visitor in that location, makes the same request, the caching server, not the origin server, sends the response. 

Dynamic acceleration

Dynamic acceleration is the reduction in server response time for dynamic web content requests because of an intermediary CDN server between the web applications and the client. Caching doesn't work well with dynamic web content because the content can change with every user request. CDN servers have to reconnect with the origin server for every dynamic request, but they accelerate the process by optimizing the connection between themselves and the origin servers.

If the client sends a dynamic request directly to the web server over the internet, the request might get lost or delayed due to network latency. Time might also be spent opening and closing the connection for security verification. On the other hand, if the nearby CDN server forwards the request to the origin server, they would already have an ongoing, trusted connection established. For example, the following features could further optimize the connection between them:

•  Intelligent routing algorithms
• Geographic proximity to the origin
• The ability to process the client request, which reduces its size

Edge logic computations

You can program the CDN edge server to perform logical computations that simplify communication between the client and server. For example, this server can do the following:

• Inspect user requests and modify caching behavior.
• Validate and handle incorrect user requests.
• Modify or optimize content before responding.

Distribution of application logic between the web servers and the network edge helps developers offload origin servers' compute requirements and improve website performance.

Amazon CloudFront is a content delivery network (CDN) service built for high performance, security, and developer convenience. You can use Amazon CloudFront to do these tasks:

• Deliver data through 450+ globally dispersed points of presence (POPs) with automated network mapping and intelligent routing.
• Improve security with traffic encryption and access controls, and use AWS Shield Standard to defend against distributed denial-of-service (DDoS) attacks at no additional charge.
• Customize the code you run at the AWS network edge using serverless compute features to balance cost, performance, and security.
• Scale automatically to deliver software, game patches, and IoT updates with high transfer rates.
  
  

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