Information Technology Reference
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reliability because problems in one application do not affect other applications or the fron-
tends.
4.3.3 Configuration Options
Splittingfunctionalityintofrontend,applicationserver,anddataservicelayersalsopermits
one to pick hardware specifically appropriate for each layer. The front-ends generally need
high network throughput and very little storage. They are also located in a special place
in the network so they have direct internet access. The application servers may be on ma-
chines that are configured differently for each application based on their needs. The data-
base service most likely has a need for large amounts of disk storage or may be a
server
tree
(as described in
Section 1.3.3
)
.
4.4 Reverse Proxy Service
A reverse proxy enables one web server to provide content from another web server trans-
parently.Theuserseesonecohesivewebsite,eventhoughitisactuallymadeupofapatch-
work of applications.
For example, suppose there is a web site that provides users with sports news, weather
reports, financial news, an email service, plus a main page:
Each of those web features is provided by a very different web service, but all of them can
be combined into a seamlessly unified user experience by a reverse proxy. Requests go to
the reverse proxy, which interprets the URL and collects the required pages from the ap-
propriate server or service. This result is then relayed to the original requester.
Like the frontend four-tier web service, this scheme permits centralizing security and
other services. Having many applications behind one domain simplifies many administrat-
ive tasks, such as maintaining per-domain crypto certificates.
The difference between a reverse proxy and the frontend of the four-tier web service is
that a reverse proxy is simpler and usually just connects the web browsers and the patch-
work of HTTP servers that sit behind it. Sometimes reverse proxies are stand-alone soft-
ware,butthefunctionalityissosimplethatitisoftenafeaturebuiltintogeneralwebserver
software.
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