Everything I can find about Software Maintenance

Given that most of us will spend most of our careers maintaining and supporting software and not building something new from scratch, there is a surprising and disappointing lack of useful information on software maintenance, on the problems that we all face in software maintenance. I’ve tried to put together here an index to useful books, articles and blog posts and white papers on software maintenance.

Last updated: November 13, 2013

Blog Posts and Articles on Software Maintenance

Jeff Atwood’s The Noble Art of Maintenance Programming is a thoughtful post on how maintenance programmers are unjustifiably unappreciated: how maintenance is much harder and more important than most people, even the people doing the work, understand.

Steve Kilner has an interesting blog called Notes on Software Maintenance. His technical focus is in maintaining RPG code on IBM iSeries computers, but he looks into a lot of basic problems and open questions in software maintenance and software maintenance management, including how to handle estimates and how to effectively manage risk and complexity in maintenance. You can get a good introduction to these problems in an article that he wrote for IBM Systems Journal, Why Good Software Goes Bad and How to Stop It and in this slideshow on Unsolved Problems in Software Maintenance.

In Sustained engineering Idiocy, Microsoft’s Eric Brechner explores how to organize your maintenance team, and the pros and cons of juggling maintenance and support responsibilities with new development work. Although some of his writing is internally Microsoft-focused, his blog is worth following for general good ideas on software development management and maintenance.

Robert Glass wrote an insightful essay on the challenges in software maintenance, "Software Maintenance is a Solution, not a Problem", in his book Software Conflict 2.0: The Art and Science of Software Engineering. You can read a copy of the essay here.

Greg Jorgensen, the Typical Programmer, shares a positive perspective on The Joys of Maintenance Programming, describing how maintenance programming can be a satisfying and successful career choice.

Steve Shaw at Intelliware wrote a short paper on his team's experience following Agile methods in software maintenance; what practices worked (short iterations, testing, prioritization, common code ownership) and what didn't (pairing, stories and story cards, stand-ups, metaphor). There is an interesting case study on Using Extreme Programming in a Maintenance Environment and another on problems with introducing Agile methods into an organization with a complex code base. A study on Introducing Agile into a large-scale maintenance organization can be downloaded from IEEE here for $19 (but $30 elsewhere at IEEE - don't ask me why).

Naresh Jain put together this slide show on why Maintenance Sucks and how to apply Agile methods to software maintenance when he was at ThoughtWorks.

The Journal of Software Maintenance and Evolution: Research and Practice regularly publishes (highly) academic papers on software maintenance and related software engineering problems.

The Good Books

There are some excellent books on writing and maintaining code, starting with Code Complete 2 by Steve McConnell: the definitive book on how to write good code, maintain it and debug it.

Legacy code means different things to different people. For some programmers, legacy code is code is any code that they didn't write. For others, it is code that stills runs on abandoned or out-of-date platforms and technologies. But everyone agrees that it is code that is difficult to understand, difficult to support and difficult to change. And in maintenance you are going to spend a lot of time dealing with it. Working Effectively with Legacy Code by Michael Feathers lays out how to get a legacy code base under control, and the steps on how to make changes safely and properly. You can follow Michael Feathers' latest work on mining source code and "brutal refactoring" on his blog.

The Passionate Programmer by Chad Fowler offers some good advice to programmers (and managers) looking for meaning in software development and maintenance.

If you are confronted with the problem of reengineering a legacy system, check out Object Oriented Reengineering Patterns, which is available free online. The pattern approach is awkward at times, but this book offers some clear guidance on when and how to reengineer a system.

More on Legacy Code

There are also a couple of good online presentations from the smart people at ThoughtWorks on how they have dealt with legacy code problems. A presentation by Matt Simons and Jonny LeRoy covers how to get a handle on existing code, mapping the code and identifying risk areas, creating dashboards to visualize the state of the code base using open source tools like Panopticode and Codecity (which offers a cool 3D cityscape view of your code, making metrics fun for everyone), or Sonar (actually, they didn’t mention Sonar, but they should have). Then they outline different strategies for incrementally re-writing large applications, emphasizing Martin Fowler’s Strangler pattern, and some examples of how they have followed these ideas with different customers.

Another good presentation from Josh Graham at ThoughtWorks on Brownfield Software walks through an interesting case study where his team came in to help with a major overhaul of a large, 10-year-old core business system.

A Team, A System, Some Legacy... And You is an intelligent and practical presentation by Eoin Woods on how an architect can make a legacy system better. How to to an architectural assessment of a legacy system, and how to improve the reliability, scalability and maintainability of the system through just enough software architecture, safe step evolution, improving testing and deployment, engaging in production, working with stakeholders and understanding the capability of the team.

Refactoring is a foundational discipline for maintenance – Martin Fowler put a name and a disciplined structure to the work that we all do, or should do, when changing code. Seriously, is there anybody who hasn’t read this book by now, who doesn’t follow some/most of these ideas in maintaining code?

Debug It! by Paul Butcher is a narrowly-focused but useful book, about debugging, problem-solving techniques, handling bugs, and writing code that is easy to debug. Especially useful for programmers new to maintenance.

Managing Maintenance

There are some great books on managing software development projects, like Steve McConnell's Rapid Development, and Scott Berkun's Making Things Happen. Many of the ideas in these books will help you in managing software maintenance work.

There are only a couple of books that take on managing software maintenance:

The best of these by far is Software Maintenance Success Recipes by Donald Reifer, a thoughtful analysis of current software maintenance practices (2012) based on the study of several large software maintenance organizations. It hilights the importance of testing in maintenance (up to 60-70% of time is spent testing and retesting changes to check for regressions, testing to reproduce bugs then testing to verify that bugs were fixed correctly...), and examines models and metrics for effectively managing maintenance.

Alain April and some other researchers have put together a Software Maintenance Maturity Model, a la the CMMI. It's obviously process-heavy and bureaucratic, but it does a thorough job of mapping out all of the work involved in software maintenance, and it's interesting in an abstract way. If you find this model useful, you can go through it in detail in the book Software Maintenance Management, although it is written by and for academics, and focuses more in defining the model than on how to deal with practical problems.

If you're managing a large enterprise maintenance team and working through a lot of structure and standards, then Thomas Pigoski's Practical Software Maintenance offers advice based on real experience - the author ran a large maintenance organization for the US Navy, and is now the CEO of TechSoft, an outsourcing firm that handles maintenance for other companies. Unfortunately this book is out of date (published 1996) and predates modern Agile and Lean methods and practices and new technologies. Pigoski also wrote the chapter on software maintenance in the IEEE SWEBOK, an academic definition of software engineering.

Another academic book which I can't recommend for practitioners is Software Maintenance: Concepts and Practice by Penny Grubb and Armstrong Takang. If you're already working in maintenance, you won't find anything here that you don't already know or that will change the way that you think or work. It's more of an introductory text for undergrad Comp Sci courses.

Studies, Statistics and Lies

Dr. Jussi Koskinen, a Comp Sci professor in Finland, maintains a useful summary of software maintenance cost data and sources.

If I want any kind of data on software development or software maintenance, the first person that I go to is Capers Jones. His book on Estimating Software Costs was last updated in 2007, and includes extensive data on software cost information and statistics and trends on software maintenance and support. Or you can read Applied Software Measurement or Software Engineering Best Practices - all of these books are built on the same comprehensive research. You can spend days going through this stuff - I have, and I keep finding interesting things.

Some of his research specific to software maintenance and legacy software is captured in an excellent white paper called Geriatric Issues of Aging Software. A couple of different versions of this paper can be found on the web, the best of them is in CrossTalk: The Journal of Defense Software Engineering dated December 2007.

One of the foundational studies on software maintenance is more than 30 years old now: Lientz and Swanson's study of software maintenance at 487 IT organizations. This study is widely referenced, and still the most comprehensive analysis of what work makes up maintenance (or at least what did in 1978). You can read a follow-up study on software maintenance management problems (1995) here. A newer (1998) but smaller study by Janice Singer looks at bugs and bug tracking, and how unimportant documentation actually is in maintenance.

Building, releasing and deploying code

And there are some good books on building, deploying and delivering code, on Continuous Integration and source code management, all of which are important in maintaining and releasing code. The best of these is the new book on Continuous Delivery by Jez Humble and David Farley. It’s full of practical advice on how to improve your code build and deployment practices; and on data migration and test automation strategies; and more far-out ideas on how far-out you can push automation in build and deployment.

Lean and Kanban and Maintenance

If you are interested in how Lean Manufacturing and Kanban ideas can be applied to software maintenance, and quite a few people are, a place to start is the XIT case study which explains how Kanban was first used to speed up and simplify management of maintenance work by a small cross-application team at Microsoft. I think there’s too much hype and religious debate around what is a conceptually simple idea (visualizing and limiting work in progress), but Kanban offers a natural framework for getting control over maintenance and support work, helping to deal with interruptions and constantly changing priorities.

Operations and DevOps

Developers need to understand how their code runs in production, need to care about and know about operations and performance and how to handle failures. This becomes even more important, more necessary, in maintenance: it’s a reality that maintenance teams face all day each day, rather than just another set of requirements for the future. Some smart people in the DevOps community are trying to come up with a more collaborative and agile way for operations and development teams to work together. Most of their work focuses on large-scale Web Operations problems and operations toolchains, but there is some good thinking here on how to improve deployment, on metrics and monitoring, and on dealing with architectural problems like scaling, and failure handling and recovery.

While helpful, most of the thinking in DevOps is being done from the operations point of view (maybe it should be called OpsDev instead…). The best book on operations problems by and for developers and software architects is still Release It! by Michael Nygard. He makes clear how important it is to, and how to, design scalable and resilient software architectures, and how and why to build an operations view into your system.

If you are working with Ops (especially in an enterprise shop) you should understand the basics of ITIL, and the cost and risks of change in production, and how to to get a production system under control. The best place to start on this is The Visible Ops Handbook, a tiny primer on intelligent IT change management.

Dealing with Data

One of the biggest problems in software maintenance is handling changes to data and data models. Scott Ambler's book Refactoring Databases walks through an incremental approach to making structural changes to database models, and how to test and deploy these changes.

Secure Software Maintenance

Dealing with security risks for legacy systems is another wormcan, and you're not going to find a lot of information to help you understand where to start, other than this set of white papers on legacy systems and COTS from Cigital, available on the US Department of Homeland Security’s Build Security In portal.

Forums and Discussion Groups

I can't find any discussion groups on software maintenance or sustaining engineering.

Stack Overflow has some interesting threads on maintenance and refactoring and other maintenance problems. It’s one of the mainstay resources for developers looking for advice on maintenance issues or anything else for that matter.

And finally...

You can learn a lot from antipatterns. How to Write Unmaintainable Code by Roedy Green is thorough, thought-provoking and fun.

I would like to hear from people about any other useful books, blogs, articles or forums that focus on software maintenance and support problems - what resources you trust, what you have found helpful.

Construx Software Executive Summit 2010

I spent a few days last week in Seattle at the Software Executive Summit hosted by Construx Software Builders. This is a small conference for senior software development managers: well organized, world class keynote speakers, and the opportunity to share ideas in supportive and open roundtables with smart and experienced people who are all focused on similar challenges, some (much) bigger, some smaller. It was good to reflect and reset, and a unique chance to spend time with some of the top thinkers in the field, swapping stories over lunch with Fred Brooks, chatting over drinks with Tim Lister and Tom DeMarco. This was my second time at this conference, and based on these experiences, I would highly recommend it to other managers looking for new ideas.

Key takeaways for me:

• A lot of people are concerned that we (software developers in general) continue to do a poor job upfront, on requirements and architecture and design. And that the push to Agile methods, on collaborative and emergent design, isn’t helping: if anything, the problem is getting worse. We are getting better and faster at developing and delivering mediocre software.


• The push for offshoring of programming and testing work continues to come mostly from the top. Even with the economic downturn, companies are having problems filling positions locally; and having problems keeping resources overseas, with turnover rates as high as 35% annually in India. The companies who are successful with offshoring make long-term commitments with outsourcing firms; invest in a lot of back-and-forth travel; rely on strong and hard-working onshore technical managers from their outsourcing partners to coordinate with their offshore teams; spend a lot of time on documentation and reviews; and spend more time and money on building and maintaining relationships. There can be real advantages at scale: for smaller companies I don’t see the return.


• Some companies have backed away from adopting Agile methods, or are running into problems with Agile projects, because the team is unwilling or unable to commit to a product roadmap or rough project definition. Customers and sponsors are frustrated, because they don’t understand what they can expect or when they can expect it. Executives don’t want to see demos: they want to know when the project will be delivered. Working in an Agile way can’t prevent you from giving the customer what they need to make business decisions and meet business commitments. This is another argument for adapting Agile methods, for doing at least some high-level design and roadmap planning upfront, agreeing on the shape of what needs to be done and on priorities before getting to work.


• Productivity: there is no clear way to define productivity or compare it across teams doing different kinds of work. Data on velocity or earned value is useful of course on bigger projects to see trends or catch problems: you want to know if you are getting faster or slower over time. Tracking time on maintenance work (bug fixes, small changes) can help to hilight technical debt or other problems: but what if most of the work that you do is maintenance? We need better ways to answer simple management questions: Am I getting my money’s worth? Is this group well-managed?


• Two of the keynote presentations looked at innovation, and two others explored related problems in design: design integrity, dealing with complexity in design. Better decisions are made by small teams, the smaller the better: the ideal team size may be just two people (Holmes and Watson). It's important to give people a safe place and time to think – uninterrupted, unstructured time, preferably time blocked off together so that people can collaborate and play off of each other's ideas. If people are always on the clock and always focused on delivery, always dealing with short-term issues, they won’t have the opportunity to come up with new ways of looking at things and better ways of working, and worse they may lose track of the bigger picture, forget to look up, forget what’s important.


• Technical debt: it’s our fault, not the business’s fault. It’s our house, so keep it clean. We have to find time to do the job right. One company uses the idea of a “tech tax”, a small (10%) overhead amount that’s included in all work for upgrades and refactoring and re-engineering.


• The importance of building business cases for technical changes like re-architecture. Remember that business cases don’t have to be solid; they just need to be reasonable. Make sure that you have some data on cost and risk, and tie your case into the larger business strategy.


• As a leader, you need to take responsibility. You have to deal with ambiguity: that's your job. Don't be a victim. Make a decision and execute.

Pen Testing - from the other side of the fence

Mike Rothman’s recent post on pen testing was interesting to me, since I come from the other side of the fence: the side of the software developers who wrote the code and the testers who test it and the project managers who are responsible for taking care of risk and the business managers who have to decide how much to spend on things like pen testing.

I’ve learned that pen testing costs and takes time to do properly, especially at the start. The time to find a good pen testing team (and there are good pen testers out there, I’ve worked with some), to understand what they do and what they need from you to do a good job. The time to setup the tests, and to setup the test system and test accounts and test data, and to harden the test system to match production-quality so that you aren’t paying an expert to report basic patching and configuration problems that you can find yourself with a Nessus scan. Sure, they are going to scan anyways, but at least save yourself and them the trouble of going through those kinds of findings.

I’ve learned that it is important to work through the testing process together, to walk through your architecture and how the important features work, to ask and answer questions so that both sides clearly understand what is going on. To make sure that the test team has enough information to focus in on what’s important, and that they are not wasting their time and your money.

To make sure that the pen tester reviews any findings with you as they go along. That if they find something important, they tell you immediately so that you can act immediately, and so that they can help verify your fix. And if they get stuck or off track, that you help them with whatever information they need to keep going.

That you will learn what it really means to think like an attacker. You might think that you are thinking like an attacker, until you see an attacker at work. The way that they probe the system, the errors and information that they find useful, the soft spots that they look for – and what they can do if they find one.

And you will learn which problems are real, exploitable. One of the arguments that you will get from a developer is whether a fault or weakness can actually be exploited. It's a valid argument – risk assessment needs to take into account how easily any vulnerability can be exploited. Pen testing helps to answer this question: if they found it, the bad guys can and probably will too. And other vulnerabilities like it.

And to work through the findings together. To understand what vulnerabilities need to be addressed and how – what’s important, what’s not. And why. What to patch now, or soon, and how to do it properly.

And finally that it’s more important to look at pen testing for what it tells you about your software and your team, than as a compliance check-mark or a quality gate. To take it seriously and really learn from anything that’s found, rather than to just fix a few bugs and move on. That you need to stop and think and look more closely at your design, and at how you build software, and consider what’s important from a risk perspective to you and your customers. And understand what you need to do to do a better job. And then do it.

It would be foolish to expect too much from pen testing in your software security program. Just like it would be foolish to expect too much from static analysis or any other technique or technology. But from my experience at least, you will get out of it what you put into it.