Set a TTL value for cached resources

Scenarios

Edge nodes respond to requests based on the cache status. If the requested resource is not cached on edge nodes, the request is redirected to the origin server to retrieve the resource. After the resource is retrieved from the origin server, an HTTP 2XX status code is returned to the edge node. The retrieved resource is cached on the edge node and returned to the client.

TTL values apply to the following scenarios:

• The resources on the origin server are updated but the cache of edge nodes is not updated.
• Requests are frequently redirected to the origin server because the resources cached on edge nodes frequently expire. This causes the cache hit ratio to decrease.
• The loading time is increased.

Usage notes

• To differentiate resources before and after they are updated on the origin server, we recommend that you use different names for resources before and after they are updated when you configure a TTL value for static resources. You can use version numbers to differentiate the resources. For example, you can use img-v1.0.jpg and img-v2.1.jpg to name a resource before and after it is updated.
• The TTL value affects the amount of network traffic redirected to the origin server. The data transfer fee varies based on the amount of back-to-origin network traffic. Set a proper TTL value based on your business requirement. A small TTL value may cause edge nodes to frequently redirect requests to the origin server and increase the amount of network traffic on the origin server.
• Cached resources that are infrequently requested may be removed before they expire.

Procedure

1. Log on to the Alibaba Cloud CDN console.
2. In the left-side navigation pane, click Domain Names.
3. On the Domain Names page, find the domain name that you want to manage and click Manage in the Actions column of the domain name.
4. In the management pane of the domain name, click Cache.
5. On the Cache Expiration tab, click Create Rule.
6. In the Create Expiration Rule dialog box, set the parameters.
   

   Parameter	Description
   Type	You can select Directory or File Extension. Select a type based on your business requirements. Directory: specifies resources that are in a specified directory. File Extension: specifies file types of resources.
   Object	If you select Directory, take note of the following rules: You can enter only one directory. You can use a forward slash (/) to specify all directories. You can enter a full path. It must start with a forward slash (/), for example, /directory/aaa. If you select File Extension, take note of the following rules: You can enter one or more file extensions and separate them with commas (,), for example, jpg,txt. File extensions are case-sensitive. You cannot use an asterisk (*) to specify all file types.
   Expire In	Specify the TTL value of the cached resources. You can set the TTL value to at most three years. Take note of the following rules: Specify a TTL value of one month or longer for static files that are infrequently updated, such as images and application packages. Specify a TTL value based on your business requirements for static files that are frequently updated, such as JavaScript and CSS files. Specify a TTL value of 0 seconds to disable caching for dynamic files, such as PHP, JSP, and ASP files.
   Weight	Specify the weight of the cache policy. The weight indicates the priority of the cache policy. Valid values are 1 to 99. A greater value indicates a higher priority. Note We recommend that you set a unique weight for each cache policy. If two cache policies are of different types but have the same weight, the cache policy that is based on file extensions has a higher priority than the other. If two cache policies are of the same type and have the same weight, the cache policies are applied in a random order. If you have created multiple cache policies for a cached resource, only the first matched rule is applied.

7. Click OK.

   After you create a cache policy, you can Modify or Delete it on the Cache Expiration tab.

Examples

Related API operations

BatchSetCdnDomainConfig