Alibaba Cloud CDN is a global network of points of presence (POPs) that are distributed across the globe. Alibaba Cloud CDN serves to reduce back-to-origin traffic. This in turn prevents network congestion and ensures that content is delivered with minimal latency across regions in various use cases.
Alibaba Cloud CDN global network is made up of more than 3,200 strategically located POPs. Among these POPs, more than 2,300 are distributed across 31 provincial regions in the Chinese mainland and more than 900 are distributed across over 70 countries and regions, including Hong Kong (China), Macao (China), and Taiwan (China). The total bandwidth capacity of Alibaba Cloud CDN can reach up to 180 Tbit/s. For more information about POP distribution, see POP distribution.
Alibaba Cloud CDN caches resources from your origin servers on POPs that are located across the globe. When customers access your resources, the resources are served from the nearest POP instead of the origin server. This helps prevent lengthy back-to-origin requests and reduces loads on origin servers, delivering a better experience to your customers and reducing back-to-origin costs. Alibaba Cloud CDN also provides IPv6 support on specific POPs.
Alibaba Cloud CDN is a simple and efficient method to deliver content to your customers. As a content provider, you can serve your content by using Alibaba Cloud CDN with just a few clicks in the console. You no longer have to worry about setting up complex configurations or modifying your code to be compatible with your content delivery provider. After you add your domain name to Alibaba Cloud CDN, your content is automatically cached to the global content delivery network. For more information about how to activate and use Alibaba Cloud CDN, see Getting started.
Benefits
You can use Alibaba Cloud CDN to separately accelerate static content 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, which eliminates network latency when traffic is passed between different ISPs.
Scalable resources: Alibaba Cloud CDN provides more than 3,200 globally distributed POPs to ensure resource scalability and service availability.
Intelligent routing: Alibaba Cloud 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 the cache hit ratio on POPs that are 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.
High bandwidth capacity: Alibaba Cloud CDN provides up to 180 Tbit/s of networking capacity.
Standardized APIs: Alibaba Cloud CDN provides a comprehensive suite of user-friendly APIs.
For more information, see Competitive advantages of Alibaba Cloud CDN.
Architecture
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. 
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.
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.
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 returned to the client. Otherwise, the request is redirected to the origin server. The retrieved resource is then served to the requester 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 supports Tianyan (an internal health monitoring system), data intelligence, and configuration management. The support system can monitor resources, analyze data, and manage configurations.
Resource monitoring: Tianyan can monitor the status of services that are running in the caching system. For example, Tianyan can monitor the number of queries per second (QPS), bandwidth, and HTTP status codes for a domain name that is accelerated by Alibaba Cloud CDN.
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 Alibaba Cloud 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.
How it works
In this example, the domain name that is accelerated by Alibaba Cloud CDN is www.aliyundoc.com. The following figure shows how Alibaba Cloud CDN handles an HTTP request from a client in Beijing. 
When the client in Beijing sends a request to retrieve resources from
www.aliyundoc.com, a domain name resolution request is sent to the local DNS server (LDNS) to retrieve the IP address ofwww.aliyundoc.com.The LDNS checks whether the cache contains the IP address that corresponds to
www.aliyundoc.com. If so, the LDNS returns the IP address to the client. If not, the website authorizes the DNS server to query the DNS records ofwww.aliyundoc.com.After the DNS server retrieves the DNS records of
www.aliyundoc.com, the DNS server returns the CNAMEwww.aliyundoc.com.example.com.The LDNS sends a request to the DNS routing system of Alibaba Cloud CDN to retrieve the DNS records of
www.aliyundoc.com.example.com. Then, the routing system selects an optimal POP on which to serve the content and returns the POP IP address to the LDNS.The LDNS receives the IP address that is returned by the routing system.
The LDNS returns the IP address to the client.
The client initiates a request to the received IP address.
If the requested resource is already cached on the POP, it is directly served to the client, as shown in Step 8.
If the requested resource is not cached on the POP or has expired, the request is redirected to the origin server. The retrieved resource is served to the client and cached on POPs based on the cache expiration rules, as shown in Step 8. For more information about how to configure a cache expiration rule, see Create a cache rule for resources.
Differences between Alibaba Cloud CDN and DCDN
Item | CDN | DCDN |
Scenario | Game updates, app updates for mobile phones, on-demand videos including long and short videos, and infographic websites. | Online shops, online payments, online chatting, online education, online multiplayer games, and financial management. |
Acceleration region |
|
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Acceleration method | Accelerates the delivery of static content and redirects requests for dynamic content to origin servers. Alibaba Cloud CDN is suitable for scenarios that require high bandwidth and process a large amount of network traffic.
| Accelerates the delivery of dynamic content, or both dynamic content and static content.
|
Supported protocol |
|
|
Scheduling mode | Supports DNS resolution, HTTPDNS, and 302 redirection. | Supports DNS resolution, HTTPDNS, and 302 redirection. |
Static content refers to the files that can be delivered without modifications or processing. The server returns the same file for different requests. Static content includes images, videos, HTML files, CSS files, JavaScript files, software installation packages, Android Package (APK) files, and compressed package files.
Dynamic content refers to the content that is delivered on a per-request basis. The server returns different contents for different requests. Dynamic content includes ASP, JSP, PHP, Perl and CGI files, API requests, and database interactive requests on websites.
For more information about static content and dynamic content, see What are static content and dynamic content?
Billing rules
Alibaba Cloud CDN generates bills for basic services and value-added services.
Billing rules of basic services: supports the pay-by-data-transfer and pay-by-peak-bandwidth metering methods. The default metering method is pay-by-data-transfer. For more information, see Billing rules of basic services.
Billing rules of value-added services: The billable items include HTTPS requests for static content, QUIC requests for static content, and real-time log entries. For more information, see Billing of value-added services.
For more information about pricing, visit the CDN pricing page.
Before you activate Alibaba Cloud CDN, we recommend that you get familiar with the billing rules of Alibaba Cloud CDN. For more information, see Activate Alibaba Cloud CDN.
Management tools
You can use your Alibaba Cloud account to manage Alibaba Cloud CDN anywhere by using the following methods:
Alibaba Cloud CDN console
The Alibaba Cloud CDN console is an easy-to-use web console that supports interactive operations. For more information, see Features and Functions and features.
Alibaba Cloud CDN API
The Alibaba Cloud CDN API is a remote procedure call (RPC) API that supports GET and POST requests. For more information, see Introduction.
Related services
The following table describes the services that are related to Alibaba Cloud CDN to help you understand the positioning of Alibaba Cloud CDN and how it can be used in combination with other Alibaba Cloud services.
Service | Purpose |
DCDN separately accelerates dynamic content and static content while balancing performance and security capabilities. | |
If you use an Object Storage Service (OSS) bucket as an origin server, you can use Alibaba Cloud CDN to accelerate content delivery and reduce Internet data transfer fees. | |
You can use Alibaba Cloud CDN together with ApsaraVideo Live to achieve media feed storage, video segmentation and transcoding, access authentication, and content delivery acceleration. | |
You can use Alibaba Cloud CDN together with ApsaraVideo VOD to reduce the buffer time and improve playback smoothness. | |
You can use Alibaba Cloud DNS that is highly available and stable to ensure smooth access to resources. | |
You can use Alibaba Cloud CDN with Elastic Compute Service (ECS) to improve website availability, protect information about origin servers, and minimize bandwidth usage costs. | |
You can specify the IP address of a Server Load Balancer (SLB) instance as the origin address to distribute traffic across multiple servers during the back-to-origin process. |
References
Alibaba Cloud CDN can be used to accelerate the delivery of content in OSS buckets or on ECS instances. The following topics describe the best practices: