Perlbal is a

Perl Perl is a high-level, general-purpose, interpreted, dynamic programming language. Though Perl is not officially an acronym, there are various backronyms in use, including "Practical Extraction and Reporting Language". Perl was developed ...

-based

reverse proxy In computer networks, a reverse proxy or surrogate server is a proxy server that appears to any client to be an ordinary web server, but in reality merely acts as an intermediary that forwards the client's requests to one or more ordinary web s ...

load balancer In computing, load balancing is the process of distributing a set of tasks over a set of resources ''Resource'' refers to all the materials available in our environment which are Technology, technologically accessible, Economics, economically ...

and

web server A web server is computer software and underlying Computer hardware, hardware that accepts requests via Hypertext Transfer Protocol, HTTP (the network protocol created to distribute web content) or its secure variant HTTPS. A user agent, co ...

. Perlbal is maintained by a group connected to Danga Interactive. The program is in common use by large web sites to distribute the load over a number of servers. Like Perl, Perlbal is distributed under both the

GNU General Public License The GNU General Public Licenses (GNU GPL or simply GPL) are a series of widely used free software licenses, or ''copyleft'' licenses, that guarantee end users the freedom to run, study, share, or modify the software. The GPL was the first ...

and the

Artistic License Artistic license (and more general or contextually-specific, derivative terms such as creative license, poetic license, historical license, dramatic license, and narrative license) refers to deviation from fact or form for artistic purposes. It ...

and is thus

free software Free software, libre software, libreware sometimes known as freedom-respecting software is computer software distributed open-source license, under terms that allow users to run the software for any purpose as well as to study, change, distribut ...

. Perlbal also features a so-called "re-proxy" mechanism. This allows a backend webapp to send back a small response to Perlbal which acts as an "internal redirect" and causes it to get the response data from elsewhere. This is often used so that expensive application server processes can defer to much simpler, faster HTTP servers to serve static files, freeing up the application server for other computing work. This is most commonly used in conjunction with MogileFS. Additionally, plugins can be written to support various operations that may traditionally have been performed at the application layer. As an example, a filter plugin has been developed that can dynamically alter the palette of a PNG or GIF image as it passes through the proxy, allowing the image to be tinted. This is used on

LiveJournal LiveJournal (), stylised as LiVEJOURNAL, is a Russian-owned social networking service where users can keep a blog, journal, or diary. American programmer Brad Fitzpatrick started LiveJournal on April 15, 1999, as a way of keeping his high school ...

to provide predefined page templates whose colors, including those "baked" into images, can be customized by the user. Doing this relatively simple filtering task at the load balancer layer avoids the overhead of passing this request back to the full application servers.

External links

Perlbal's homepage

Google Code Archive

The Perl Programming Language

References

{{Perl Reverse proxy Free web server software Perl software Free software programmed in Perl