The Architecture of Open Source Applications (Volume 2)

Amy Brown and Greg Wilson

In the introduction to Volume 1 of this series, we wrote:

Building architecture and software architecture have a lot in common, but there is one crucial difference. While architects study thousands of buildings in their training and during their careers, most software developers only ever get to know a handful of large programs well… As a result, they repeat one another's mistakes rather than building on one another's successes… This book is our attempt to change that.

In the year since that book appeared, over two dozen people have worked hard to create the sequel you have in your hands. They have done so because they believe, as we do, that software design can and should be taught by example—that the best way to learn how think like an expert is to study how experts think. From web servers and compilers through health record management systems to the infrastructure that Mozilla uses to get Firefox out the door, there are lessons all around us. We hope that by collecting some of them together in this book, we can help you become a better developer.

— Amy Brown and Greg Wilson


Andrew Alexeev (nginx): Andrew is a co-founder of Nginx, Inc.—the company behind nginx. Prior to joining Nginx, Inc. at the beginning of 2011, Andrew worked in the Internet industry and in a variety of ICT divisions for enterprises. Andrew holds a diploma in Electronics from St. Petersburg Electrotechnical University and an executive MBA from Antwerp Management School.

Chris AtLee (Firefox Release Engineering): Chris is loving his job managing Release Engineers at Mozilla. He has a BMath in Computer Science from the University of Waterloo. His online ramblings can be found at

Michael Bayer (SQLAlchemy): Michael Bayer has been working with open source software and databases since the mid-1990s. Today he's active in the Python community, working to spread good software practices to an ever wider audience. Follow Mike on Twitter at @zzzeek.

Lukas Blakk (Firefox Release Engineering): Lukas graduated from Toronto's Seneca College with a bachelor of Software Development in 2009, but started working with Mozilla's Release Engineering team while still a student thanks to Dave Humphrey's ( Topics in Open Source classes. Lukas Blakk's adventures with open source can be followed on her blog at

Amy Brown (editorial): Amy worked in the software industry for ten years before quitting to create a freelance editing and book production business. She has an underused degree in Math from the University of Waterloo. She can be found online at

Michael Droettboom (matplotlib): Michael Droettboom works for STScI developing science and calibration software for the Hubble and James Webb Space Telescopes. He has worked on the matplotlib project since 2007.

Elizabeth Flanagan (Yocto): Elizabeth Flanagan works for the Open Source Technologies Center at Intel Corp as the Yocto Project's Build and Release engineer. She is the maintainer of the Yocto Autobuilder and contributes to the Yocto Project and OE-Core. She lives in Portland, Oregon and can be found online at

Jeff Hardy (The Dynamic Language Runtime and the Iron Languages): Jeff started programming in high school, which led to a bachelor's degree in Software Engineering from the University of Alberta and his current position writing Python code for in Seattle. He has also led IronPython's development since 2010. You can find more information about him at

Sumana Harihareswara (MediaWiki): Sumana is the community manager for MediaWiki as the volunteer development coordinator for the Wikimedia Foundation. She previously worked with the GNOME, Empathy, Telepathy, Miro, and AltLaw projects. Sumana is an advisory board member for the Ada Initiative, which supports women in open technology and culture. She lives in New York City. Her personal site is at

Tim Hunt (Moodle): Tim Hunt started out as a mathematician, getting as far as a PhD in non-linear dynamics from the University of Cambridge before deciding to do something a bit less esoteric with his life. He now works as a Leading Software Developer at the Open University in Milton Keynes, UK, working on their learning and teaching systems which are based on Moodle. Since 2006 he has been the maintainer of the Moodle quiz module and the question bank code, a role he still enjoys. From 2008 to 2009, Tim spent a year in Australia working at the Moodle HQ offices. He blogs at and can be found @tim_hunt on Twitter.

John Hunter (matplotlib): John Hunter is a Quantitative Analyst at TradeLink Securities. He received his doctorate in neurobiology at the University of Chicago for experimental and numerical modeling work on synchronization, and continued his work on synchronization processes as a postdoc in Neurology working on epilepsy. He left academia for quantitative finance in 2005. An avid Python programmer and lecturer in scientific computing in Python, he is original author and lead developer of the scientific visualization package matplotlib.

Luis Ibáñez (ITK): Luis has worked for 12 years on the development of the Insight Toolkit (ITK), an open source library for medical imaging analysis. Luis is a strong supporter of open access and the revival of reproducibility verification in scientific publishing. Luis has been teaching a course on Open Source Software Practices at Rensselaer Polytechnic Institute since 2007.

Mike Kamermans (Processing.js): Mike started his career in computer science by failing technical Computer Science and promptly moved on to getting a master's degree in Artificial Intelligence, instead. He's been programming in order not to have to program since 1998, with a focus on getting people the tools they need to get the jobs they need done, done. He has focussed on many other things as well, including writing a book on Japanese grammar, and writing a detailed explanation of the math behind Bézier curves. His under-used home page is at

Luke Kanies (Puppet): Luke founded Puppet and Puppet Labs in 2005 out of fear and desperation, with the goal of producing better operations tools and changing how we manage systems. He has been publishing and speaking on his work in Unix administration since 1997, focusing on development since 2001. He has developed and published multiple simple sysadmin tools and contributed to established products like Cfengine, and has presented on Puppet and other tools around the world, including at OSCON, LISA,, and His work with Puppet has been an important part of DevOps and delivering on the promise of cloud computing.

Brad King (ITK): Brad King joined Kitware as a founding member of the Software Process group. He earned a PhD in Computer Science from Rensselaer Polytechnic Institute. He is one of the original developers of the Insight Toolkit (ITK), an open source library for medical imaging analysis. At Kitware Dr. King's work focuses on methods and tools for open source software development. He is a core developer of CMake and has made contributions to many open source projects including VTK and ParaView.

Simon Marlow (The Glasgow Haskell Compiler): Simon Marlow is a developer at Microsoft Research's Cambridge lab, and for the last 14 years has been doing research and development using Haskell. He is one of the lead developers of the Glasgow Haskell Compiler, and amongst other things is responsible for its runtime system. Recently, Simon's main focus has been on providing great support for concurrent and parallel programming with Haskell. Simon can be reached via @simonmar on Twitter, or +Simon Marlow on Google+.

Kate Matsudaira (Scalable Web Architecture and Distributed Systems): Kate Matsudaira has worked as the VP Engineering/CTO at several technology startups, including currently at Decide, and formerly at SEOmoz and Delve Networks (acquired by Limelight). Prior to joining the startup world she spent time as a software engineer and technical lead/manager at Amazon and Microsoft. Kate has hands-on knowledge and experience with building large scale distributed web systems, big data, cloud computing and technical leadership. Kate has a BS in Computer Science from Harvey Mudd College, and has completed graduate work at the University of Washington in both Business and Computer Science (MS). You can read more on her blog and website

Jessica McKellar (Twisted): Jessica is a software engineer from Boston, MA. She is a Twisted maintainer, Python Software Foundation member, and an organizer for the Boston Python user group. She can be found online at

John O'Duinn (Firefox Release Engineering): John has led Mozilla's Release Engineering group since May 2007. In that time, he's led work to streamline Mozilla's release mechanics, improve developer productivity—and do it all while also making the lives of Release Engineers better. John got involved in Release Engineering 19 years ago when he shipped software that reintroduced a bug that had been fixed in a previous release. John's blog is at

Guillaume Paumier (MediaWiki): Guillaume is Technical Communications Manager at the Wikimedia Foundation, the nonprofit behind Wikipedia and MediaWiki. A Wikipedia photographer and editor since 2005, Guillaume is the author of a Wikipedia handbook in French. He also holds an engineering degree in Physics and a PhD in microsystems for life sciences. His home online is at

Benjamin Peterson (PyPy): Benjamin contributes to CPython and PyPy as well as several Python libraries. In general, he is interested in compilers and interpreters, particularly for dynamic languages. Outside of programming, he enjoys music (clarinet, piano, and composition), pure math, German literature, and great food. His website is

Simon Peyton Jones (The Glasgow Haskell Compiler): Simon Peyton Jones is a researcher at Microsoft Research Cambridge, before which he was a professor of computer science at Glasgow University. Inspired by the elegance of purely-functional programming when he was a student, Simon has focused nearly thirty years of research on pursuing that idea to see where it leads. Haskell is his first baby, and still forms the platform for much of his research.

Susan Potter (Git): Susan is a polyglot software developer with a penchant for skepticism. She has been designing, developing and deploying distributed trading services and applications since 1996, recently switching to building multi-tenant systems for software firms. Susan is a passionate power user of Git, Linux, and Vim. You can find her tweeting random thoughts on Erlang, Haskell, Scala, and (of course) Git @SusanPotter.

Eric Raymond (GPSD): Eric S. Raymond is a wandering anthropologist and trouble-making philosopher. He's written some code, too. If you're not laughing by now, why are you reading this book?

Jennifer Ruttan (OSCAR): Jennifer Ruttan lives in Toronto. Since graduating from the University of Toronto with a degree in Computer Science, she has worked as a software engineer for Indivica, a company devoted to improving patient health care through the use of new technology. Follow her on Twitter @jenruttan.

Stan Shebs (GDB): Stan has had open source as his day job since 1989, when a colleague at Apple needed a compiler to generate code for an experimental VM and GCC 1.31 was conveniently at hand. After following up with the oft-disbelieved Mac System 7 port of GCC (it was the experiment's control case), Stan went to Cygnus Support, where he maintained GDB for the FSF and helped on many embedded tools projects. Returning to Apple in 2000, he worked on GCC and GDB for Mac OS X. A short time at Mozilla preceded a jump to CodeSourcery, now part of Mentor Graphics, where he continues to develop new features for GDB. Stan's professorial tone is explained by his PhD in Computer Science from the University of Utah.

Michael Snoyman (Yesod): Michael Snoyman received his BS in Mathematics from UCLA. After working as an actuary in the US, he moved to Israel and began a career in web development. In order to produce high-performance, robust sites quickly, he created the Yesod Web Framework and its associated libraries.

Jeffrey M. Squyres (Open MPI): Jeff works in the rack server division at Cisco; he is Cisco's representative to the MPI Forum standards body and is a chapter author of the MPI-2 standard. Jeff is Cisco's core software developer in the open source Open MPI project. He has worked in the High Performance Computing (HPC) field since his early graduate-student days in the mid-1990s. After some active duty tours in the military, Jeff received his doctorate in Computer Science and Engineering from the University of Notre Dame in 2004. He blogs about High Performance Computing Networking.

Martin Sústrik (ZeroMQ): Martin Sústrik is an expert in the field of messaging middleware, and participated in the creation and reference implementation of the AMQP standard. He has been involved in various messaging projects in the financial industry. He is a founder of the ØMQ project, and currently is working on integration of messaging technology with operating systems and the Internet stack. He can be reached at, and on Twitter as @sustrik.

Christopher Svec (FreeRTOS): Chris is an embedded software engineer who currently develops firmware for low power wireless chips. In a previous life he designed x86 processors, which comes in handy more often than you'd think when working on non-x86 processors. Chris has bachelor's and master's degrees in Electrical and Computer Engineering, both from Purdue University. He lives in Boston with his wife and golden retriever. You can find him on the web at

Barry Warsaw (GNU Mailman): Barry Warsaw is the project leader for GNU Mailman. He has been a core Python developer since 1995, and release manager for several Python versions. He currently works for Canonical as a software engineer on the Ubuntu Platform Foundations team. He can be reached at or @pumpichank on Twitter. His home page is

Greg Wilson (editorial): Greg has worked over the past 25 years in high-performance scientific computing, data visualization, and computer security, and is the author or editor of several computing books (including the 2008 Jolt Award winner Beautiful Code) and two books for children. Greg received a PhD in Computer Science from the University of Edinburgh in 1993.

Armen Zambrano Gasparnian (Firefox Release Engineering): Armen has been working for Mozilla since 2008 as a Release Engineer. He has worked on releases, developers' infrastructure optimization and localization. Armen works with youth at the Church on the Rock, Toronto, and has worked with international Christian non-profits for years. Armen has a bachelor in Software Development from Seneca College and has taken a few years of Computer Science at the University of Malaga. He blogs at


We would like to thank Google for their support of Amy Brown's work on this project, and Cat Allman for arranging it. We would also like to thank all of our technical reviewers:

Johan Harjono Justin Sheehy Nikita Pchelin
Laurie McDougall Sookraj Tom Plaskon Greg Lapouchnian
Will Schroeder Bill Hoffman Audrey Tang
James Crook Todd Ritchie Josh McCarthy
Andrew Petersen Pascal Rapicault Eric Aderhold
Jonathan Deber Trevor Bekolay Taavi Burns
Tina Yee Colin Morris Christian Muise
David Scannell Victor Ng Blake Winton
Kim Moir Simon Stewart Jonathan Dursi
Richard Barry Ric Holt Maria Khomenko
Erick Dransch Ian Bull Ellen Hsiang

especially Tavish Armstrong and Trevor Bekolay, without whose above-and-beyond assistance this book would have taken a lot longer to produce. Thanks also to everyone who offered to review but was unable to for various reasons, and to everyone else who helped and supported the production of this book.

Thank you also to James Howe (, who kindly let us use his picture of New York's Equitable Building for the cover.


Dozens of volunteers worked hard to create this book, but there is still a lot to do. You can help by reporting errors, helping to translate the content into other languages, or describing the architecture of other open source projects. Please contact us at if you would like to get involved.