Cache Purge

Last updated: 2020-01-19 15:49:26

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Feature Overview

CDN is capable of configuring basic cache. Cache expiration time can be configured according to rules such as specified business types, directories, and specific URLs to regularly purge resources cached on nodes, pull latest resources from the origin server and cache them again.

In addition, CDN can purge cache for specified URLs or directories in batches:

  • Purge URL: Delete the cache of corresponding resources on all CDN nodes.
  • Purge directory: if you select the "Purge Changed Resources" mode, when an end user accesses a resource under the corresponding directory, the Last-Modify information of the resource will be obtained from the origin-pull. If it is the same as that of the currently cached resource, the cached resource will be directly returned; otherwise, the changed resource will be pulled from the origin server and cached again. If you select the "Purge All Resources" mode, when the user accesses a resource under the corresponding directory, the latest version of the resource will be directly pulled from the origin server and cached again.

After a purge is successfully executed, the corresponding resource on the node does not have a valid cache. When the user initiates an access request again, the node will pull the required resource from the origin server and cache it on the node again. If you submit a large number of purge tasks, many caches will be cleared, resulting in a surge in origin-pull requests and high pressure on the origin server.

Use Cases

New resource release

After a resource is overwritten by a new one with the same name on the origin server, to prevent users on the entire network from accessing the legacy version of the resource cached on the node, you can submit a request to purge the URL/directory for the resource and clear all caches so users can directly access the latest version of the resource.

Illegal resource cleanup

When illegal resources (such as resources related to pornography, drug, or gambling) are found on your origin server, they may still be accessible even after you delete them on the origin server because of node cache. To protect your network environment security, you can delete the cached resources through URL purge for timely cleanup.

Operation Guide

How to use

Log in to the CDN Console, click Purge and Prefetch on the left sidebar, and submit a Purge URL or Purge Directory task:



In the History section, you can query tasks by specified time period, keyword, and purge task type. With regard to keyword, you can only query tasks by specifying a domain name or a complete purged URL/directory:

The console can return up to 10,000 operation records at a time, which can be exported to Excel. If you have a high number of purge tasks, please query and export them in batches.

Precautions

URL purge:

  • Up to 10,000 URLs can be purged per day for each account, and up to 1,000 URLs can be submitted for purge at a time. For users who have activated GCD, up to 10,000 global URLs can be purged per day, which are independent of URL purge quotas in China.
  • You need to add the http:// or https:// protocol identifier when submitting a purge task.
  • URLs in the format of http://*.test.com/ cannot be purged. Even if you connect a wildcard domain name to CDN, you need to submit the corresponding sub-domain names for purge.
  • When submitting URLs for purge, domain names should have already been connected to CDN; otherwise, the submission will fail.
  • URLs containing Chinese characters cannot be purged.
  • By default, URLs will be purged by acceleration regions of domain names in the URLs.

Directory Purge:

  • Up to 100 directories can be purged per day per account, and up to 20 directories can be submitted for purge at a time. For users who have activated GCD, up to 100 global directories can be purged per day, which are independent of directory quotas in China.
  • You need to add the http:// or https:// protocol identifier when submitting a purge task.
  • Directories in the format of http://*.test.com/ cannot be purged. Therefore, even if you connect a wildcard domain name to CDN, you need to submit the corresponding sub-domain names for purge.
  • When submitting URLs for purge, domain names should have already been connected to CDN; otherwise, the submission will fail.
  • URL directories containing Chinese characters cannot be purged.

Sub-user permissions configuration:

  • The operations of directory purge, URL purge, and purge history query must have already been connected to the latest permission system and support permission configuration at the resource (domain name) level.
  • For permission assignment method, please see Permission Configuration.

Use Cases

Directory purge - purge changed resources

The acceleration domain name is purge-test-1251991073.file.myqcloud.com, the origin server is Tencent Cloud Object Storage (COS), and resources on the origin server are as follows:

  1. Initiate requests to access resources 1.txt and 2.txt respectively. Nodes to be hit can be determined based on X-Cache-Lookup: Hit From Distank3 and Server: NWS_SPMid, resources will be directly returned by the nodes:

  2. On the origin server, replace 1.txt with a file that has the same name, and the file’s last modified time changes, while 2.txt stays the same:

  3. Initiate requests again. As the cache has not expired, the legacy content of the 1.txt resource will be accessed:
  4. Submit a directory purge task, select Purge Changed Resources, and wait for the purge to complete:
  5. After the purge is completed, because Last-Modified of 1.txt has been changed, the request will be forwarded to the origin server. As 2.txt has not been changed, even after a directory purge task is submitted, it will still be hit by nodes and returned: