what is a cdn?

Date: May 23, 2023

Abstract: A CDN (Content Delivery Network) supply a fast, stable and customizable content delivery service for accelerated content distribution to users worldwide.This article will introduce the advantages, architecture, application scenarios, etc. of Alibaba Cloud CDN

A CDN is a network of servers that work together to distribute content to users. The content is cached or stored on each server, making it readily available to users. When a user requests content, the CDN routes the request to the nearest server, reducing latency and improving website speed.

CDN supports large file delivery, hybrid acceleration of dynamic and static content delivery, data transmission using non-standard protocols, programmable computing, and end-to-end IPv6. A wide range of CDN solutions developed based on practical experience are available for various business scenarios, such as application store downloads, e-commerce promotions, online education, financial security, social communication, game acceleration, and multimedia streaming.

You can use Alibaba Cloud CDN to separately accelerate static and dynamic content. Alibaba Cloud CDN provides the following benefits:

• Globally distributed POPs: Alibaba Cloud CDN redirects requests to the nearest POPs that belong to the same Internet service provider (ISP) as the clients, eliminating network latency when traffic is passed between different ISPs.

• Intelligent routing: CDN monitors the health status of POPs in real time, and redirects requests to optimal POPs selected by the routing system based on client locations and ISPs.

• Intelligent connections: Alibaba Cloud CDN uses optimization strategies such as protocol optimization and connection optimization to reduce network latency and accelerate content delivery, especially over networks with limited connectivity.

• Intelligent caching: Alibaba Cloud CDN caches popular content across its global network, improving cache hit ratio on POPs closest to clients.

• Lower IT costs: Aside from content delivery capabilities, POPs also provide computing, bandwidth, and networking capabilities, which you can make use of to reduce investment in IT hardware.

• Standardized APIs: Alibaba Cloud CDN provides a comprehensive suite of user-friendly APIs.

The following figure shows the architecture of Alibaba Cloud CDN. Alibaba Cloud CDN consists of a routing system, a route quality system, a caching system, and a support system.



• Routing system

The routing system provides a policy center and supports Domain Name System (DNS) resolution, HTTPDNS, and 302 redirection. When a client sends a request, the request is resolved by DNS resolution and subsequently processed by the routing system.

• Route quality system

The route quality system monitors the loads and health status of POPs and routes in real time. This information is shared with the routing system, which uses this information to select optimal routes for requests. The routing system also takes additional information included in the origin IP address, such as the ISP and region of the requests, into account when selecting the optimal route.

• Caching system

The caching system redirects requests to POPs based on the access points where the requests originate. If the requested resource is already cached on the POPs, the resource is directly served to the client. Otherwise, the request is redirected to the origin server. The retrieved resource is then served to the clients and cached on the POPs. Subsequent requests for the resources are served through the POPs. Alibaba Cloud CDN uses intelligent object algorithms to cache content based on popularity in a multi-level cache. This mechanism allows Alibaba Cloud CDN to reduce the amount of bandwidth resources consumed by back-to-origin routing, and improve user experience.

• Support system

The support system can monitor resources, analyze data, and manage configurations.

Data analytics: You can analyze data, such as the top N most frequently requested URLs, page views (PVs), and unique visitors (UVs) for a domain name that is accelerated by CDN.

Configuration management: You can create and manage cache expiration rules to improve the efficiency of the caching system. For example, you can create a cache expiration rule for a specified type of file or enable parameter filtering.

The application scenario of CDN (Content Delivery Network) is to improve the speed and reliability of delivering web content to users across the globe. CDN