CDN:What is Alibaba Cloud CDN?

Alibaba Cloud CDN helps you accelerate the delivery of static resources and improve resource access speeds:

• Extensive POP resources: Provides users with nearby access from the same ISP, which resolves latency and speed issues caused by long-distance or cross-ISP access.

• Elastic scalability: Built on a global network of over 3,200 POPs, CDN allows for elastic resource scaling to ensure high availability for your business.

• Intelligent Scheduling System: Monitors the health of POPs in real time and assigns the optimal access POP based on the user's location and ISP for optimal performance.

• Smart routing: Uses techniques such as protocol and connection optimization to reduce overall latency and increase transfer speeds, especially in weak network conditions.

• Efficient caching strategies: Achieves a higher cache hit ratio by serving content from nearby POPs, improving access speed.

• Reduced IT costs: Offloads your business's computing, bandwidth, and connection requirements to the edge, which lowers your IT costs.

• High bandwidth capacity: The total network bandwidth capacity is 180 Tbps.

• Standard APIs: Provides industry-standard APIs for improved usability and compatibility.

CDN accelerates content delivery by handling your domain's DNS resolution. It intelligently routes user requests to the nearest POP. If the requested resource is already cached at this POP, the POP delivers it directly to the user without a request to the origin server.

Assume your accelerated domain name is www.aliyundoc.com. After you enable the CDN service, the process is as follows when an end user in Singapore sends an HTTP request.

1. User initiates a request: The end user requests a resource from www.aliyundoc.com. This request first goes to the local DNS for the domain's IP address.

2. DNS forwards the request: The local DNS checks its cache for an IP address record for www.aliyundoc.com. If a record exists, the local DNS returns it to the user. If not, the local DNS queries the authoritative DNS for the domain's resolution record.

3. CNAME record takes effect: After the authoritative DNS resolves www.aliyundoc.com, it returns the CNAME record www.aliyundoc.com.example.com.

4. Smart scheduling: The local DNS sends a resolution request for www.aliyundoc.com.example.com to the CDN routing system, which then assigns the optimal POP IP address.

5. POP IP is returned: The local DNS receives the optimal POP IP address from CDN.

6. User accesses the POP: The Local DNS returns the optimal POP IP address to the user. The user then sends a request for the resource to this POP IP address.

7. POP responds:

   • Cache Hit: If the POP has the requested resource cached, it returns the resource directly to the user, completing the request.

   • Cache Miss: If the POP does not have the resource cached, or if the cached resource has expired, the POP requests the resource from the origin server. After the POP retrieves the resource, it caches it based on your configured caching rules and returns it to the user, completing the request. For information about how to configure caching policies, see Configure a time-to-live (TTL) for a cached file.

The following diagram shows the architecture of Alibaba Cloud CDN, which consists of four major systems: route quality, routing, cache, and support.

• Route quality system

  The route quality system monitors the real-time load and health of all POPs and routes in the cache system. It sends this information to the routing system. The routing system obtains the user's ISP and region from the user's IP address and combines this information with the route quality data to assign an optimal POP to the user requests.

• Routing system

  This system supports multiple routing modes, including policy-based, DNS, DNS-over-HTTPS (DoH), and 302 redirect. When an end user initiates a request, it first undergoes DNS resolution, and then is processed by the CDN routing system.

• Cache system

  The user accesses the cache POP that is assigned as the optimal access POP. If the POP has the requested resource cached, the resource is returned. If neither the L1 (edge) POP nor the L2 (regional) POP has the resource cached, an origin request is sent to retrieve the resource. The resource is then cached in the system for subsequent user requests, avoiding repeated origin traffic. This multi-tiered caching architecture improves content delivery efficiency, reduces origin bandwidth, and enhances user experience.

• Support system

  The support system includes Tianyan, data intelligence, and a configuration management system. They provide resource monitoring, data analytics, and configuration management capabilities.

  • Resource monitoring: Tianyan can monitor the running status of user services on the caching system. For example, it monitors common metrics for CDN-accelerated domain names, such as queries per second (QPS), bandwidth, and HTTP status codes.

  • Data analytics: You can analyze data for CDN-accelerated domain names, such as top URLs, page views (PVs), and unique visitors (UVs).

  • Configuration management: The configuration management system lets you configure cache rules, such as cache file types and ignoring query parameters during caching, to improve the operational efficiency of the caching system.

CDN billing includes basic and value-added services:

• Billing of basic services: This includes two billing methods: pay-by-traffic and pay-by-peak-bandwidth. The default method is pay-by-traffic. For more details, see Billing of basic services.

• Billing of value-added services: Billable items for value-added services include the number of static HTTPS requests, static QUIC requests, and real-time log deliveries. For more details, see Billing of value-added services.

After creating and logging on to an Alibaba Cloud account, you can manage CDN from anywhere using these tools:

• Manage in the CDN console

  The management console is a web-based service page with interactive, easy-to-use UI. For information about console operations, see User Guide.

• Manage by using APIs

  CDN supports RPC API operations that support GET and POST requests. For API documentations, see API Reference.

Learn about services related to CDN to better understand its role and use cases within the Alibaba Cloud ecosystem ecosystem.

To learn about specific use cases for CDN, see the following topics:

• Deliver OSS content faster with CDN

• Use Alibaba Cloud CDN to accelerate the retrieval of resources from an ECS instance

• Increase the cache hit ratios of Alibaba Cloud CDN