HP Cache Server Appliance Administrator Guide

The idea behind web proxy caching is to store copies of frequently accessed documents close to users and

serve this information to them on demand. Internet users get their information faster and Internet bandwidth

is freed up for other tasks.

This chapter discusses the following topics.

• Understanding web proxy caching‚ on page 11

• News article caching‚ on page 16

Understanding web proxy caching

Internet users direct their requests to web servers all over the Internet. For a caching server to serve these

requests,itmustactasaweb proxy server. A web proxy server fields user requests to arbitrary web servers

and either serves the requests, or forwards them on to the origin server (the web server that contains the

original copy of the requested information).

The Traffic Server proxy supports both transparent proxy caching, where the user’s client software (typically

a browser) is unaware that it is communicating with a proxy, and explicit proxy caching, where the user’s

client software must be configured to send requests directly to the traffic Server proxy.

A day in the life of a cache request

Here is an overview of the steps that take place as a Traffic Server proxy cache serves a user request.

1. Traffic Server receives a user request for a document, image, news article, or other web object.

2. With the object address in hand, Traffic Server looks up the requested object in its object database (cache).

3. If the object is in the cache, Traffic Server checks to see if the object is fresh enough to serve. (See

Ensuring cached object freshness‚ on page 12 for details.) If the object is fresh, Traffic Server serves it to

the user as a cache hit (Figure 3-1.).

Figure 3-1. A cache hit

4. If the data in the cache is stale, Traffic Server connects to the origin server and asks if the document is still

fresh. If the document is still fresh, Traffic Server sends the cached copy to the user immediately.

3 Web Proxy Caching

cache

local

request

a cache hit

returned document

Traffic Server

hit

client