This topic describes the terms of Alibaba Cloud CDN. These terms help you better understand and use Alibaba Cloud CDN.

Origin server

An origin server refers to the server where your workloads are running. An origin server can process and respond to user requests. If the requested content is not cached on edge nodes, the request is redirected to the origin server to retrieve the content. Alibaba Cloud CDN supports the following types of origin server address: Object Storage Service (OSS) endpoints, IP addresses of origin servers, domain names of origin servers, and Function Compute domain names.

Edge node

An edge node is where resources from origin servers are cached. Edge nodes are deployed in different regions to accelerate content delivery. In the documents of Alibaba Cloud CDN, an edge node is also called a CDN node, a cache node, an acceleration node, or an Alibaba Cloud node.

Accelerated domain name

A domain name, also known as a network domain, is an identification string that defines one or more Internet resources, such as computers. A domain name is a numerical address, sometimes also represents the physical location.

An accelerated domain refers to a domain name that is accelerated by Alibaba Cloud CDN and accessed by users. Alibaba Cloud CDN retrieves resources from origin servers and caches them on edge nodes. This accelerates content delivery. For example, if you add www.example.com to Alibaba Cloud CDN, www.example.com is an accelerated domain name. In the documents of Alibaba Cloud CDN, an accelerated domain name is also called a domain name.

CNAME record

A Canonical Name (CNAME) record is also called an alias record that is used to map a domain name to another domain name, which is the domain name of the origin server.

For example, you have a server that stores a large amount of data and the server uses the domain name example.aliyundoc.com. However, you also want to use the domain name demo.aliyundoc.com to access the data. In this case, you can add a CNAME record in the system of your DNS service provider to map demo.aliyundoc.com to example.aliyundoc.com. After you add the CNAME record, all requests that are sent to demo.aliyundoc.com are redirected to example.aliyundoc.com.

CNAME

After you add a domain name to Alibaba Cloud CDN, the domain name is assigned a CNAME. The CNAME is in the format of *.*kunlun*.com. You must add a CNAME record in the system of your service provider to map the domain name to its CNAME. After the CNAME record takes effect, all requests sent to the domain name are redirected to edge nodes. This accelerates content delivery.

Static content (static resources)

Static content refers to content that remains unchanged no matter how many times it is requested by users. Static content includes images, videos, web files such as HTML, CSS, and JavaScript files, software installation packages, APK files, and compressed files.

Alibaba Cloud CDN caches static content from origin servers to the globally distributed edge nodes. Users can retrieve static content from the nearest edge nodes. This accelerates content delivery.

Dynamic content (dynamic resources)

Dynamic content refers to content that may change for different requests. Dynamic content includes web files such as ASP, JSP, PHP, PERL, and CGI files, API operations, and interactive requests to databases.

Alibaba Cloud CDN accelerates the delivery of only static content. If you want to accelerate the delivery of dynamic content, you can use Dynamic Route for CDN (DCDN). For more information, see What is DCDN?

DNS

Domain Name System (DNS) is a service used to resolve domain names to the corresponding IP addresses that can be recognized by machines. Domain names are easy-to-identify to humans but machines identify only IP addresses. Each domain name is resolved to a unique IP address. DNS resolution resolves a domain name to the corresponding IP address. This way, users can visit your website through its domain name. A dedicated DNS server is used to automatically resolve domain names to the corresponding IP addresses. For example, if you enter www.example.com into the address bar of your browser, the DNS server automatically resolves the domain name to 220.181.112.143(for example).

Alibaba Cloud also provides a DNS resolution service called Alibaba Cloud DNS. For more information, see Alibaba Cloud DNS.

SSL/TLS

Secure Sockets Layer (SSL) is a secure communication protocol that improves the integrity and security of data transmitted over the Internet. SSL encryption is implemented between the TCP/IP protocol stack and application layer protocols. After SSL is standardized, its name is changed to Transport Layer Security (TLS), which is a cryptographic protocol on the transport layer. Therefore, SSL and TLS are collectively known as SSL/TLS.

Back-to-origin

If the resources requested by a request are not cached on edge nodes or have expired on edge nodes, the request is redirected to the origin server to retrieve the resources. This process is called back-to-origin.

Origin host

An origin host refers to a domain name hosted on an origin server. If the origin server hosts multiple domain names, requests are redirected to a specific domain name. Examples:
  • Example 1: The origin server uses a domain name.

    If the origin server is set to example-origin.com and the origin host is set to www.example.com, requests are redirected to www.example.com that is hosted on the origin server example-origin.com.

  • Example 2: The origin server uses an IP address.

    If the origin server is set to 10.10.10.10 and the origin host is set to www.example.com, requests are redirected to www.example.com that is hosted on the origin server 10.10.10.10.

Origin protocol policy

An origin protocol policy specifies the protocol that is used to redirect requests to origin servers. An origin protocol policy can specify whether requests are redirected to origin servers over the protocol used by the clients. For example, if a client sends an HTTP request for content that is not cached on the edge nodes, the edge node can redirect the request to the origin server also over HTTP.

Parameter filtering

Parameter filtering is a feature provided by Alibaba Cloud CDN. You can enable or disable this feature to specify whether to ignore the parameters that follow the question mark (?) in the URL of each request when Alibaba Cloud CDN caches content from the origin server. The rules are:
  • After parameter filtering is enabled, edge nodes ignore the parameters that follow the question mark (?) in URLs to retrieve content from the origin server. Then, edge nodes cache one version of the retrieved content and all subsequent requests retrieve this version from the edge nodes.
  • After parameter filtering is disabled, edge nodes cache a version of the requested content for each request with a unique URL that includes parameters.

If URLs with different parameters point to the same resource, we recommend that you enable this feature to increase the cache hit ratio.