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CHAPTER 12: PRELOADING CONTENT
Introduction
The Preload Content Feature enables the administrator and other
authorized users to preload required sites onto the Webcache before they
are requested. These preloads can be done manually or run on a schedule
outside working hours and enable you to store content in the Webcache
that you know will be required by a client’s Web browser.
Preloading content will not cache dynamic Web pages such as those
served from Web searches or those pages disallowed by use of a
robots.txt file.
As part of these preloads, the administrator may also specify a content
lifetime for the Web pages that are preloaded. The Content Lifetime
ensures that the content, once preloaded is guaranteed to be a cache hit
for a period of time. The lifetime rules will override any server HTTP cache
control directives (excluding dynamic content and pages marked
‘no-cache’ by the Web server), and remove the need for any freshness
checks by the Webcache itself.
Cache Control settings take precedence over Content Preload. If a site is
marked as Never Cache in Cache Control then it will never be cached
even if Content Preload gives it a Cache Lifetime.
Advantages and
Disadvantages of
Preloading Content
Preloading content results in a faster response time for the clients of the
Webcache and less activity across your Internet connection. Any request
made for a Web page within its Content Lifetime will not result in any
traffic external to your network as the Webcache is able to serve the page
from the cached content. Additionally, preload tasks can be scheduled
when your network is quietest, for example by using spare WAN
bandwidth at night.
When preloading content, care needs to be taken with the Content
Lifetime that is set. A site that is accessed within its Content Lifetime will
be served from the Webcache without reference to the origin server.
Preloading a daily news Web site with a Content Lifetime of one week
will result in your users seeing the same day’s news for the seven day
period. Even pinning the content for a day will result in your users missing
out on any news flashes and possibly seeing the previous days news if the
content is preloaded before the site is refreshed.
In summary, preloading content:
■
Saves the WAN bandwidth of your network.