Reverse proxy

A reverse proxy is a proxy server that is installed within the neighborhood of one or more servers. Typically, reverse proxies are utilized in front of webservers. All connections coming from the Internet addressed to one of the webservers are routed through the proxy server, which may either deal with the request itself or pass the request wholly or partially to the main webservers.

A reverse proxy dispatches in-bound network traffic to a set of servers, presenting a single interface to the caller. For example, a reverse proxy could be used for load balancing a cluster of web servers. In contrast, a forward proxy acts as a proxy for out-bound traffic. For example, an ISP may use a proxy to forward HTTP traffic from its clients to external web servers on the internet; it may also cache the results to improve performance.

There are several reasons for installing reverse proxy servers:

Security: the proxy server is an additional layer of defense and therefore protects the webservers further up the chain
Encryption / SSL acceleration: when secure websites are created, the SSL encryption is sometimes not done by the webserver itself, but by a reverse proxy that is equipped with SSL acceleration hardware.
Load distribution: the reverse proxy can distribute the load to several servers, each server serving its own application area. In the case of reverse proxying in the neighborhood of webservers, the reverse proxy may have to rewrite the URLs in each webpage (translation from externally known URLs to the internal locations).
Caching static content: A reverse proxy can offload the webservers by caching static content, such as images. Proxy caches of this sort can often satisfy a considerable amount of website requests, greatly reducing the load on the central web server.
Compression: the proxy server can optimize and compress the content to speed up the load time.
Spoon feeding: a dynamically generated page can be produced all at once and served to the reverse-proxy, which can then return it to the client a little bit at a time. The program that generates the page is not forced to remain open and tying up server resources during the possibly extended time the client requires to complete the transfer.

Proxy server
Varnish is a modern open source reverse proxy.
Squid cache is a proxy server software that may be installed in a reverse proxy configuration.
The Apache HTTP Server may be extended with mod_proxy to be used as a reverse proxy; a caching proxy server may be configured using the mod_cache module in conjunction with mod_proxy
Perlbal is a Perl-based reverse proxy load balancer and web server.
Lighttpd can be used as a reverse proxy with load balancing capabilities.
Nginx - Web and Reverse proxy server.
Pound, a lightweight open source reverse proxy.

See also