Feature Overview

Cache TTL specifies the time period after which an origin server resource cached on CDN points of presence (POPs) expires. After the preset TTL ends, CDN POPs label the corresponding resource cache as expired. In this case, if a client requests the resource from a CDN POP, CDN sends a request with the If-Modified-Since header or If-None-Match header to the origin server to check whether the content is updated. If updated, CDN obtains the updated content and caches the content to a CDN POP. You can configure the cache TTL for a static resource based on your business requirements by specifying a path or filename extension.

Additional Considerations

You can modify the default cache configurations recommended by eSurfing Cloud as needed. The following figure shows the recommended configurations.

If you delete the recommended configurations and add no other configurations, CDN will honor origin's cache headers for caching, including the Pragama:no-cache, Cache-Control, and Expires response headers. The priorities of these headers are sorted in descending order as follows: Pragama: no-cache, Cache-Control: no-cache/private/no-store > Cache-Control: max-age=n (n≥0)> Expires. If none of the preceding cache headers is given by the origin server, the resources are not cached to CDN POPs.
If a cached file/content is rarely requested by end users within a period of time, the cahced file may be erased before the TTL ends due to the limits of disk storage. This means even if you set a large TTL for a file, such as one month, there is still a possibility that the requests of the file is passed to origin within one month.
The maximum cache TTL is 3 year (1095 days) on an eSurfing Cloud CDN POP.

Procedure

Log in to the CDN console.
Go to Domain Management -> Domain List page.
On the Domain List page, find the target domain name, and click Edit in the Actions column.
Click Cache .
ClickAdd and setup the cache rules as you need.

1)Select a type. You can select Filename extension , Directory , Homepage , All files , or Absolute file path and configure corresponding settings.

• Filename extension: filename extensions. For example, if you enter mp4 or flv into the Content field, it specifies files suffixed with .mp4 or .flv.

• Directory: a specific directory. For example, /a/ specifies files in the /a/ directory.

• Homepage: domain name homepage. The value is fixed to /.

• All files: all files from a domain name. The value is fixed to /.

• Absolute file path: a file specified by a URI. For example, /a/b.js means the cache rule applies to the b.js file in the /a/ directory specified in the request URL, regardless of whether a query string is carried.

2)Select a cache rule. The default value is Force cache .

• If you select Force cache , CDN POPs cache files based on the preset rule and time, regardless of the cache headers returned by the origin server, such as Cache-Control: no-cache/no-store/private and Cache-Control: max-age=n (n>0). Cache-Control: no-cache/no-store/private means that the files are not cached, and Cache-Control: max-age=n (n>0) means that the files are cached. **Note:** If you select **Force cache** and set **Expire In** to **0** , CDN POPs do not cache the file, regardless of how the origin server responds.

• If you select Origin first , the directive from the origin server prevails for the cache TTL if the origin server returns the response headers Cache-Control: no-cache/no-store/private, Cache-Control: max-age=n (n>0), or Expires. Cache-Control: no-cache/no-store/private means that the file is not cached.

• If you select Do not cache , CDN POPs do not cache the file, regardless of the cache-related response headers returned by the origin server.

3)Select unit for TTL (Seconds, minutes, hours, days) and set the time.

4)By default, the Ignore Query Strings When Caching feature is enabled. If query strings need to be carried when caching, disable the feature.

Note: Typically, a CDN POP uses the original URL of a user request as the cache key for a file that can be cached. The cache key is the unique ID of the file cached on the CDN POP. If the original URLs carry query strings and different parameters in the query strings specify the same file, you can enable the feature for ignoring query strings when caching. After this feature is enabled, CDN POPs use URLs without query strings as cache keys. This helps increase the cache hit ratio and reduce the number of back-to-origin requests. If the original URLs carry query strings and different parameters in the query strings cause the origin server to point to different files, disable this feature to avoid caching errors.

5)Select a weight. This parameter specifies the priority. You can set the weight to customize the priority. A larger weight indicates a higher priority. A URL may match different cache rules. For example, a URL matches both a filename extension cache rule and a directory cache rule. In this case, the cache rule with a larger weight applies.

Click OK and Save.

Example

If you need to cache .txt files for 7 days and ignore Cache-Control response headers from the origin server, add a cache rule as shown below. When adding the rule, enter txt in the Content field, set the cache TTL to 7 days, and select Force cache .

Content Delivery Network

Cache TTL