Perlbal is a

Perl Perl is a family of two High-level programming language, high-level, General-purpose programming language, general-purpose, Interpreter (computing), interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it ...

-based

reverse proxy In computer networks, a reverse proxy is the application that sits in front of back-end applications and forwards client (e.g. browser) requests to those applications. Reverse proxies help increase scalability, performance, resilience and securi ...

load balancer In computing, load balancing is the process of distributing a set of tasks over a set of resources (computing units), with the aim of making their overall processing more efficient. Load balancing can optimize the response time and avoid unevenl ...

and

web server A web server is computer software and underlying hardware that accepts requests via HTTP (the network protocol created to distribute web content) or its secure variant HTTPS. A user agent, commonly a web browser or web crawler, initi ...

. 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 License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end user In product development, an end user (sometimes end-user) is a person who ultimately uses or is intended to ulti ...

and the

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

and is thus

free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, ...

. 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 (russian: Живой Журнал), 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, ...

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