Uses of Reverse Proxy

We are all aware of proxy servers, that enable us to access the internet from inside a firewall. These proxies are known as forward proxies. Similarly we have reverse proxy that sits in front of a webserver and can provide caching and also redirection.

Recently, we needed to expose a website to the internet. I thought the only way of doing it would be to assign a new IP to the webserver machine and have a DNS setup for it. Alternatively, we can put in one more NIC card and have that IP address exposed to the public.

But Reverse Proxy presents us with an interesting alternative. A reverse proxy can be used to enable controlled access from the Web at large to servers behind a firewall.
Here is a simple example provided at the Apache website (Apache can also be used as a reverse proxy server)

Scenario:
Company example.com has a website at www.example.com, which has a public IP address and DNS entry can be accessed from anywhere on the Internet.

The company also has a couple of application servers which have private IP addresses and unregistered DNS entries, and are inside the firewall. The application servers are visible within the network - including the webserver, as "internal1.example.com" and "internal2.example.com", But because they have no public DNS entries, anyone looking at internal1.example.com from outside the company network will get a "no such host" error.

A decision is taken to enable Web access to the application servers. But they should not be exposed to the Internet directly, instead they should be integrated with the webserver, so that http://www.example.com/app1/any-path-here is mapped internally to http://internal1.example.com/any-path-here and http://www.example.com/app2/other-path-here is mapped internally to http://internal2.example.com/other-path-here. This is a typical reverse-proxy situation.
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In my scenario, my network admin guys were able to put my website on the internet without touching my server even once :)

For more information on reverse proxy check out the following links:
http://www.apacheweek.com/features/reverseproxies
http://www.informit.com/articles/article.asp?p=169534&rl=1
http://en.wikipedia.org/wiki/Reverse_proxy