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Chapter 3
Web Proxy Caching
Transparency
NNTP traffic bound for a well known NNTP server can be intercepted transparently by Traffic Server. By
transparently intercepting, caching, and serving the NNTP data from a centralized parent news server, Traffic
Server simplifies migration and administration while increasing responsiveness and decreasing network
utilization.
Transparency mode is installed by default during Traffic Server installation. See the HP Web Cache Server
Appliance Getting Started Guide for more information. Once installed, you will need to configure and enable
it to be able to use it.
Posting
Traffic Server sends user article postings to the parent news server. You can specify the parent news server
that receives postings for a particular group or set of groups in the
nntp_servers.config
file; see page 177.
When Traffic Server acts as the news server (accepting article feeds), Traffic Server accepts postings.
With background posting, the Traffic Server queues posted articles until the posting news server can accept
the posted article.
Maintaining the cache: updates and feeds
Traffic Server can maintain the freshness of its cache by:
•
Updating its cache on demand
•
Actively retrieving (pulling) updates at configurable intervals
•
Accepting news feeds
The
nntp_servers.config
file controls the Traffic Server’s caching behavior for specific news groups; see
page 177 for more information. You configure update frequencies in the Configure: Protocols page of Traffic
Manager. Here are the available options:
•
Pull the overview information for specified groups
For all groups designated as pullover, the server will retrieve the overview database information (using the
OVER
/
XOVER
commands) automatically and periodically.
Pulling overview information can be useful for high volume groups which are frequently read but from
which only a subset of the articles are accessed.
•
Pull the articles for specified groups
For all groups designated as pull, Traffic Server retrieves the articles automatically and periodically.
Pulling groups is useful when the administrator does not wish to or cannot set up a full or partial feed.
•
Dynamically subscribe to specified groups
Traffic Server can monitor the usage pattern for groups, and those for which the overview database is very
frequently accessed can be treated as pullover groups. Likewise those for which the articles are very
frequently accessed can be treated as pull groups.
•
Take a partial feed (push) for specified groups
For all groups designated as push, Traffic Server verifies that it has any requested articles and retrieves
them from the parent server if they are not available locally.
Partial feeds are useful for groups where some articles are always accessed, or for shifting article transport
to a time of day when bandwidth is cheaper or underutilized.