Edge Security Acceleration:Custom Cachekey

Background information

• The custom cache key feature does not modify the back-to-origin URL. It only modifies the cache identity of the request. This ensures that the back-to-origin request is consistent with the client request.

• A cache key is the unique identifier for a file cached on an ESA point of presence (POP). Each file cached on a POP has a unique cache key. By default, the cache key is the complete URL of the client request, including parameters.

Use cases

Use case 1: Unify cache keys

A customer's request URLs contain complex parameters. Consequently, even when multiple requests access the same file, the ESA POP treats them as requests for different files because of the varying URL parameters. The POP then caches them as multiple files, which increases the number of back-to-origin requests.

To resolve this issue, you can use the custom cache key feature to ignore query strings. This unifies the cache keys for the same class of requests and reduces the back-to-origin rate.

Use case 2: Differentiate cache keys

When client request URLs are identical, ESA treats them as requests for the same file. However, the client field in the HTTP request header can distinguish between different client systems. This indicates that different files are being requested.

In this case, you can use the custom cache key feature to generate different cache keys based on the client type. This ensures that the two requests are identified by two different cache keys.

Procedure

After you add a rule, when a user requests a resource, ESA matches and executes rules sequentially based on the rule execution priority.

1. In the ESA console, choose Websites. In the Website column, click the target site.

2. In the navigation pane on the left, choose Rules > Cache Rules.

3. Click Create Rule and enter a Rule Name.

4. In the If requests match... section, configure the conditions that a request must match. For more information, see Composition of a rule expression.

5. In the Cache Eligibility section, set Cache Eligibility to Eligible for Cache.

6. In the Custom Cache Keys section, click Configure, and set the following parameters.

   

   Parameter	Description
   Sort Query Strings	Specifies whether to enable the Sort Query String feature.
   Query String	Specifies whether to remove the ? and the subsequent query string from the request URL.
   HTTP Request Header	Include Header Names and Their Values: Adds the specified HTTP request header names and their values to the Cachekey. Check Presence of: Checks whether the specified HTTP request headers exist. If they exist, their names are added to the Cachekey.
   Cookie	Include Cookie Names and Their Values: Adds the specified cookie parameter names and their values to the Cachekey. Check Presence of: Checks whether the specified cookie parameters exist. If they exist, their names are added to the Cachekey.
   User	Device Type: Identifies the client type based on the User-Agent information of the client and then generates a Cachekey based on the client type. Country/Region: Identifies the country or region of the client based on the client IP address and then generates a Cachekey based on the country or region. Language: Identifies the client language based on the Accept-Language information in the client request and then generates a Cachekey based on the language type.
   Cache Deception Defense	Defends against web cache deception attacks while allowing static content to be cached.

7. Click OK.

Configuration examples

References

Rule-related features vary in execution priority, rule behavior, and configuration scope. For more information, see How ESA rules take effect.