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Chapter 7
Hierarchical Caching
Figure 7-1. An HTTP cache hierarchy in action
Parent failover
Traffic Server supports the use of several parent caches so that if one parent cache is not available, another
parent cache can service client requests.
When you configure your Traffic Server to use more than one parent cache, Traffic Server detects when a
parent is not available and sends missed requests to another parent cache. If you specify more than two parent
caches, the order in which the parent caches are queried depends upon the parent proxy rules configured in the
parent configuration file described in
parent.config‚ on page 179
. By default, the parent caches are queried in
the order in which they are listed in the configuration file.
Configuring Traffic Server to use an HTTP parent cache
To configure Traffic Server to use one or more parent caches, you must:
•
Enable the HTTP parent caching option (described in Chapter , “Enabling the HTTP parent caching
option,” below)
•
Identify the HTTP parent cache(s) you want to use to service missed requests (described in
Identifying
HTTP parent caches‚ on page 53
)
Enabling the HTTP parent caching option
You can enable the HTTP parent caching option by using Traffic Manager or by editing a configuration file
manually. Both procedures are described below.
To enable the HTTP parent caching option from Traffic Manager:
1. Access Traffic Manager from your browser (refer to
Accessing Traffic Manager‚ on page 8
).
2. On the Configure tab, click the Routing button.
NOTE
If the request is a cache miss on the parent, the parent retrieves the content from the
origin server (or from another cache depending on the parent’s configuration). The
parent caches the content, then sends a copy to the Traffic Server (its child), where it is
cached and served to the client.
cache
regional
miss
cache
local
request
forwarded request
returned
document
Baltimore
traffic server
New York
traffic server
hit
parent cache
1
2
3
end user
