Chapter 6
• Content based on the User-Agent and Accept-Encoding values. The RAM cache holds different content for Vary headers. The items that the RAM cache does not cache are: • Private data specified by cache control headers • HEAD, PUT, DELETE, TRACE, and CONNECT methods, by default
Understanding the RAM Cache mechanism The default RAM cache configuration caches only responses to HTTP GET methods. However, you can use the RAM cache to cache other methods, too, including non-HTTP methods. You do this by specifying a URI in the URI Include or Pin list within an HTTP profile, or by writing an iRule. The remainder of the section answers the following questions: • Which responses does the BIG-IP system actually cache? • What is the effect of adding URIs to the Include List in the HTTP profile? • What is the order of preference that the BIG-IP system uses when processing the Pin List, Include List, and Exclude List?
Which responses does the BIG-IP system cache? The BIG-IP system determines which responses to cache by evaluating both the HTTP request and the response. Table 6.8 shows the criteria within both a request and a response that the system uses before determining whether to include or exclude a response from the cache. Criteria
Action
When
The system invokes a CACHE::disable command within an HTTP_REQUEST event.
Exclude
Always
The request matches an item in the Exclude list of the HTTP profile.
Exclude
Always
HTTP Request Criteria
The request matches an item in the Pin list of the HTTP profile.
Include
Always
The request matches an item in the Include list of the HTTP profile.
Include
Always
The request specifies a method other than GET, including non-standard HTTP methods.
Exclude
Always, except when overridden by an item in the Pin or Include lists, or by an iRule.
The BIG-IP system processes an iRule triggered by the CACHE_REQUEST event.
Include
Always
HTTP Response Criteria
Table 6.8 Request and response criteria for determining whether to cache a response
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