Specifications

Chapter 4: Configuring the High-Level Network
4-62
Cache statements
A cache statement may be either the only statement in a rule or it may be
nested within an if statement. Rules with cache statements are used to select
pools based on HTTP header data. Table 4.12 describes the cache statement
syntax.
For a description of pool selection based on HTTP header data, see Pool
selection based on HTTP header data, on page 4-56.
Configuring rules
You can create rules from the command line or by using the Configuration
utility. Each of these methods is described in this section.
To define a rule using the Configuration utility
1. In the navigation pane, click Rules.
This opens the Rules screen.
Rule Syntax Description
expression A Boolean expression setting the condition or conditions under which the rule applies.
origin_pool <pool_name> This required attribute specifies a pool of servers with all the content to which requests
are load balanced when the requested content is not cacheable or when all the cache
servers are unavailable or when you use a BIG-IP to redirect a miss request from a
cache.
cache_pool <pool_name> This required attribute specifies a pool of cache servers to which requests are directed
to optimize cache performance.
hot_pool <pool_name> This optional attribute specifies a pool of servers that contain content to which requests
are load balanced when the requested content is frequently requested (hot). If you
specify any of the following attributes in this table, the hot_pool attribute is required.
hot_threshold <hit_rate> This optional attribute specifies the minimum number of requests for content that
cause the content to change from cool to hot at the end of the period (hit_period).
cool_threshold <hit_rate> This optional attribute specifies the maximum number of requests for specified content
that cause the content to change from hot to cool at the end of the period.
hit_period <seconds> This optional attribute specifies the period in seconds over which to count requests for
particular content before deciding whether to change the hot or cool state of the
content.
content_hash_size
<sets_in_content_hash>
This optional attribute specifies the number subsets into which the content is divided
when calculating whether content is hot or cool. The requests for all content in the
same subset are summed and a single hot or cool state is assigned to each subset.
This attribute should be within the same order of magnitude as the actual number of
requests possible. For example, if the entire site is composed of 500,000 pieces of
content, a content_hash_size of 100,000 would be typical.
Table 4.12 Description of cache statement syntax