Feature Introduction

When CDN nodes retrieve resources from the origin server, the origin server returns a response status code. For special status codes such as 4xx and 5xx, you can configure the expiration time for status codes on eSurfing Cloud CDN. When the client requests the same resource again within the TTL, the CDN will directly respond with the status code without triggering an origin request, reducing the pressure on the origin server. If the caching duration of the status code on the CDN exceeds the TTL, the cached status code will expire, and the request for the same resource will require an origin request. For more details, please refer to: Cache TTL for HTTP status code. If you prefer the cache headers from the origin server to have higher priority when the origin server responds with special status codes and carries related cache headers, and only apply the CDN-set expiration time when there are no relevant cache headers, you can configure the Cache TTL for HTTP status code (honor origin version).

After configuring the Cache TTL for HTTP status code (honor origin version), the scenarios for different cache headers returned by the origin server for 4xx or 5xx status codes are as follows:

When the origin server responds with Pragma: no-cache, Cache-Control: no-cache/no-store/private, or other non-caching headers, after configuring the Cache TTL for HTTP status code (honor origin version), the corresponding special status codes will not be cached.
When the origin server responds with Cache-Control: max-age=n: If n is greater than 0, the CDN will follow the caching expiration time set by the origin server and will not trigger a back-to-origin request within the unexpired period. If n is equal to 0, the CDN will consider the cache as expired and perform a back-to-origin validation.
When the origin server responds with Expires: If the Expires time is greater than the current time, the CDN will follow the caching expiration time set by the origin server and will not trigger a back-to-origin request within the TTL. If Expires is less than or equal to the current time, the CDN will consider the cache as expired and perform a back-to-origin validation.
If the origin server does not return any of the above cache-related response headers, the CDN-configured caching expiration time will be used. For example, if 5s is configured, within 5 seconds after the CDN acquires a special status code from the origin server, requests for the same resource will not trigger a back-to-origin request, and the special status code will be returned directly.

Note

If the origin server responds with headers mentioned in 1, 2, and 3 simultaneously, the priority order is as follows: Pragma: no-cache, Cache-Control: no-cache/no-store/private, and other non-caching headers > Cache-Control: max-age=n > Expires.

Configurations

This feature is not self-serviceable for now. If you need to enable it, please contact our customer support team via hotline (852)31000000 or email global.noc@chinatelecomglobal.com for manual activation.

The following info should be clarified:

Parameters	Descriptions
Status Code	for example, 4xx, 5xx
TTL	The cache time duration on CDN

Content Delivery Network

Cache TTL for HTTP status code (honor origin version)