It wasn't that long ago that agile development methods such as eXtreme Programming (XP), Dynamic Systems Development Method (DSDM), or Scrum were introduced as new and somewhat controversial methods for delivering software development projects. Today, agile development practices such as iterative development, test-driven development, and continuous integration are commonplace and have been accepted and absorbed as an alternative approach to software development. Whatever your beliefs or experience, you cannot deny that agile development projects can and have proved successful in delivering functionality on time and to budget.1
This article discusses a specific aspect of agile development -- the concept of Agile Software Configuration Management, or Agile SCM, a well-designed, light form of SCM that can be used by software development projects practicing agile development methods. As part of this discussion, I will also look at how an enterprise SCM toolset, such as the IBM Rational SCM toolset, can be implemented to support agile projects.
The approach that most agile development methods share is the direct involvement and interaction with users or customers, and the development of functionality in frequent, short iterations (typically two to twelve weeks). Typically, at the start of each iteration, agile teams negotiate with the customer to define new features or change requests. These are estimated by the developers and then subsequently prioritized by the customer for the next iteration, as illustrated in Figure 1. A backlog of any features or change requests that have not been implemented in an iteration are kept and, together with any new requests, are re-prioritized by the customer for the next iteration. Developers are permitted to work on requests for the current iteration or to carry out re-factoring and simplification of existing code as necessary. The intention behind this is to keep design simple and prevent gratuitous feature bloat. Code is also continuously integrated; it is implemented, tested, and committed frequently in very small units, with an automated build process being invoked at commit time to check for integration errors.
Figure 1: At the start of each iteration, agile teams negotiate with the customer to define new features or change requests. These are estimated by the developers and then subsequently prioritized by the customer for the next iteration.
Like any software development process, agile development methods require a core and supporting team-based environment, something which has traditionally been called software configuration management, or SCM. Unfortunately, some practitioners regard SCM as an archaic and unnecessarily controlling discipline. But this is a misconception. While it is true that too much and the wrong kind of SCM can strangle an agile development project, it is also true that agile practices such as iterative development and continuous integration simply couldn't function without SCM.
So, just how much and what form of SCM do you need for these types of projects? To answer these questions, let us introduce a relatively new concept: Agile SCM.
Agile SCM as a concept in its own right was probably first discussed in detail by Brad Appleton and Stephen Berczuk in their book Software Configuration Management Patterns and on the SCM portal CM Crossroads.2 One of their observations was that:
...Configuration Management is going to be critical "fulcrum" in leveraging a balanced and effective set of SCM processes and criteria for agile development methods. With such a large emphasis on lean and lightweight from the "agilists," CM on agile projects will need to be less intrusive/invasive (what Grady Booch would call low-friction) to allow agile projects to succeed while at the same time not being so minimal (due to overreaction) as to contribute to their failure.
Which concurs with my earlier point that, although SCM on agile projects tends to be more lightweight and less visible, SCM itself is a critical requirement of such projects. It is perhaps no coincidence that the majority of agile projects adopt entry-level or lightweight SCM tools such as CVS, Subversion, or BitKeeper -- tools that have limited but ultimately sufficient functionality for agile projects. They are also tools that tend to be less intrusive and value the development experience, rather than a high-level conformance to a regimented process.
In theory, however, there is no reason why you can't use any SCM tool to support agile development practices. You certainly don't have to use all the features of a tool, and most tools allow some degree of process customization, from heavyweight to lightweight and all places in between. With enterprise tools such as IBM Rational ClearCase, some organizations are tempted to use all the "bells and whistles" to define a heavyweight SCM process simply because the tool can support it. However, such a process won't necessarily meet the requirements of your project. To find the right process and level of customization, you should first identify and define your requirements, which means understanding exactly what your development process is, or should be, and then determining how SCM can support it.
In general, SCM is about "governance" of the development process; that is, SCM allows projects to retain a measure of control, but at the same time allows developers the freedom to create within the process. With agile development methods, developers typically have a high degree of freedom and authority to implement changes. However, one consequence of continuous integration and test-driven development practices is that they actually enable a well-disciplined and almost self-governing approach for SCM. For example, on every code change, agile developers must first write a unit test, then write sufficient code just to make the test work, and then subsequently refactor as necessary to complete the change. The code change is committed (or checked in), and its unit tests become part of the integration suite. Any side-effects of the change are made immediately visible through the integration build mechanism compiling and executing the complete unit test suite -- any problems that are found can be fixed immediately.
In Agile SCM, this governance model is a natural part of day-to-day development activities and in all consequence is pretty much transparent to the developers. To understand this governance model in more detail, let us look at some different characteristics of SCM and how they would typically be implemented to support agile development methods:
- Branches. Agile projects implement simple branching strategies, typically an Active Development Line3 and a Release Prep Line. The Active Development Line is used by developers to commit their changes and is the means by which continuous integration builds are carried out. The Release Prep Line is used to stabilize or engineer a release before making it available to customers; developers are typically not allowed to commit changes to it.
- Workspaces. Developers typically have a single private workspace initially pointing at the collective set of latest versions of the Active Development Line. Their workspaces are updated at a minimum when they start work on a new feature or change request and just before they commit their changes to the Active Development Line to check for integration issues.
- Labels. As with traditional SCM, labels are placed at significant milestones on a collective set of code versions, at a minimum on every release build, so that it is possible to reproduce a build environment if necessary.
- Builds and integration. An automated build process is a key factor of successful agile development. The build process typically monitors the Active Development Line for commits and, if found, automatically executes, after a grace period, an integration build and unit test. Notification of the success or failure of this build is a key communication factor in agile teams.
- Change control. As discussed earlier, there is an implicit authorization process with agile development teams; developers are authorized to make changes based on customer priority or refactoring as necessary. Requests are recorded either in change control systems, or even for more informal projects, particularly within eXtreme Programming projects, on cards or flip charts.
Although SCM characteristics such as these are typical in agile processes, they are just as likely to be "tuned" depending on the amount of agility that a particular project requires. For example, some projects might not be able to build on each commit but instead initiate a single daily or nightly integration build. Also, projects don't exist in isolation; they are normally one of many projects in an organization. Often, an enterprise organization contains a mix of both agile and traditional plan-driven projects, and thus a given project may exist in a particular market segment. This enterprise context often is the strongest factor in deciding which SCM toolset is chosen and which additional aspects of governance the chosen toolset will need to support.
If you took a single agile project in isolation, its SCM requirements could almost certainly be met by a relatively simple toolset. Such a toolset would probably be used and administered within the project itself. However, rather than supporting project-specific toolsets, most large organizations prefer to standardize on a single SCM toolset and develop organizational processes around it. There are typically two main reasons for doing this:
- To reduce the total cost of ownership of the toolset and its processes
- To be able to conform to a desired (or mandatory) compliance or regulatory framework
Total cost of ownership is often a subjective issue, since it includes many quantifiable aspects such as license, administration, and support costs, as well as other subjective aspects such as capability or scalability. Enterprise toolsets such as the IBM Rational toolset often have higher licensing, administration, and support costs (certainly initially), but if implemented correctly, these enterprise toolsets can increase organizational capability as a whole. They also have proven scalability, with a single, consolidated infrastructure able to support large, geographically dispersed development organizations. As noted above, the main danger of such a toolset is the temptation to use more functionality than is necessary, which can strangle agile projects. An organizational SCM framework will need to be established, and its implementation should be in some way configurable so as to meet the needs of different projects.
Recent industry regulations such as Sarbanes Oxley, Basel II, and CFR 21 Part 11 can place onerous overheads on SCM processes, particularly with respect to change control. Although practices such as "segregation of duties" -- not allowing developers to deploy to live environments -- should be implemented, the rigorous enforcement of change control on agile projects can strangle them. The business cost of not meeting these regulations is massive, however, so while agile projects might want to avoid non-essential governance practices, they have to accept some additional overhead in most cases. The good news is that if implemented correctly, an automated SCM toolset can take on most of this governance aspect, allowing businesses to maintain organizational control, while allowing individual projects and their developers to work on the creative aspect of developing new software functionality to solve business problems.
Let's consider how a balance between governance rigor and agility can be achieved for agile projects using the IBM Rational toolset.
There is a common misconception that an enterprise SCM toolset -- such as the IBM Rational toolset -- cannot be used to support the implementation of agile development methods. The significant functionality in these toolsets is provided to support many different types and sizes of development environments; consequently, it is not always easy to identify which elements of this functionality should be used, and there is a danger that the SCM process will be over-engineered. Today, there is no out-of-the-box agile SCM configuration for the IBM Rational SCM toolset. Instead, it is left to the implementers of the toolset to find the appropriate configuration to meet their needs.
The good news is that many organizations have managed to find such a configuration and are successfully implementing agile development methods underpinned by the IBM Rational toolset. From observation, there are a number of best practices that these projects share. Although these best practices are not absolute, they should be enough to give you a framework and starting point for implementing your own agile SCM process. They can be summarized as follows:
- Implement a simplified branching strategy. Agile projects implement simple branching strategies. In both Base ClearCase and ClearCase UCM (Unified Change Management), branches ("streams" in UCM terms) can be created easily and cheaply. There is therefore often a temptation to define a more complex branching strategy than is strictly necessary. Agile projects actively encourage continuous integration and refactoring, but if developers are isolated on a branch, problematic or complex merges can occur. This is particularly true in the case of namespace refactoring (renaming, adding, or deleting files or directories). Consequently, most agile projects implement a specific branch to act as the Active Development Line and which the developers work on directly. In Base ClearCase, this is either the main branch or a specific project integration branch; in UCM, this is the UCM project's integration stream. To isolate an environment for a release, a Release-Prep Line is also typically implemented. This is achieved by creating a release branch (or UCM stream) off of a candidate label (or UCM baseline) that has been placed down on the Active Development Line. This label will be created either manually -- or more likely automatically -- as part of an integration build. A diagram illustrating this structure is provided in Figure 2.
Figure 2: To isolate an environment for a release, a Release-Prep Line is achieved by creating a release branch (or UCM stream) off of a candidate label (or UCM baseline) that has been placed down on the Active Development Line. This label will be created either manually -- or more likely automatically -- as part of an integration build.
As well as a simplified branching strategy, agile projects also tend to configure ClearCase to default to an "unreserved" checkout model. This allows developers to check out and check in a file on the Active Development Line at any point (although they might be required to do some merging if another developer has also checked out and in the same file in the interim). The default ClearCase model is for the first check out to be "reserved." This means that you are guaranteed to be able to check the element back in without having to do a merge. However, it also means that others can't check out the element reserved until you put it back and that people who check out the element unreserved have to wait for you to check it back in before they can merge. Such an approach really goes against agile principles.
- Use snapshot-view developer workspaces. If developers are to work on a single branch, then dynamic views are not really an option. The power of dynamic views is that they update themselves automatically when the branch that they are looking on is updated. Therefore, if a number of developers have dynamic views onto a single branch, they will have little control or isolation in their workspace. Although developer branches could be implemented, as we have discussed, this can lead to other issues. Agile projects therefore typically implement snapshot views, where the developers are able to update their workspace to bring in changes from other developers. In practice, this allows developers enough control and isolation.
- Automate the build process. Single branch development and incremental check-in can only work when automated builds and tests are executed frequently. Most agile projects configure their build process to execute on every developer check-in. As well as compiling code, such a build process also validates new code to see if it conforms to pre-defined coding conventions and executes unit tests where necessary. In agile development methods, this practice is often called continuous integration. Its desired result is to expose integration problems as early as possible so that they are easy to address, and also to have a built, tested, and potentially releasable build at every stage of the project. Continuous integration is often intricately linked with the practice of test-driven development. This is because developers need to implement unit tests for all aspects of their code to validate not only that the build has been compiled, but also that it conforms to some minimum level of functional quality. In ClearCase terms, the agile project's build process is set to monitor the integration branch (or UCM stream) and then execute a build script on check-in. This is typically carried out by build execution tools such as CruiseControl (http://cruisecontrol.sourceforge.net) or IBM Rational BuildForge (http://www-306.ibm.com/software/rational/buildmanagement/).4
- Stage and re-use pre-built binaries. Building any reasonably complex software application can take time, from several minutes to several hours. In agile projects, developers will be delivering and integrating small changes frequently; they therefore obviously cannot wait for a two-hour build to complete before getting feedback. To avoid this situation, agile projects typically "stage" and re-use pre-built binaries, and only rebuild the whole system when necessary (for example, nightly or weekly). There are a number of ways of staging binaries. ClearCase is often used to stage binaries, with labels or baselines placed down on related versions to indicate a composite set of re-usable binaries. For C/C++ projects, the ClearCase clearmake utility also has a build-avoidance mechanism that can be used to automate much of this staging and re-use process, although there is little evidence of agile projects using this mechanism. For Java projects, an alternate approach is to stage pre-built libraries in a dependency management tool such as Ivy (http://jayasoft.org/ivy) or Maven (http://maven.apache.org). This is particularly appropriate where a project re-uses a significant amount of open-source components or where there are issues with transitive dependencies (i.e., where libraries are dependent on other libraries).
- Release as a composite application. When it comes to releasing your application, try to release all your files rather than releasing individual sets. Most agile projects prefer to deploy the whole or composite application each time rather than just the individual files that have changed. Although this is not a hard and fast rule, releasing the whole application in the same way each time tends to make the process more repeatable and prevents problems with missing files. This practice is more important for agile projects than more high-ceremony projects, because they produce an executable, testable, and releasable application at the end of every iteration. Obviously, this depends on the target environment for the application. If it is Web portal, then this approach is fine, but if it is a consumer application (running on, say, Microsoft Windows), then a full release cannot be made to the customer each time a patch is required.
- Limit the use of MultiSite technology. Distributed agile projects require unrestricted access to a single codeline. The ClearCase MultiSite technology replicates complete databases from site to site. To avoid conflicting changes being made at each site, it implements a concept called mastership. This means that if a project is being worked on across multiple sites and developers are sharing the same branch, then mastership has to be requested by each developer before they can commit their changes. There are a number of ways to work around this issue (including creating site-based integration branches), but they all add an extra level of complexity and can slow down the development process. For these reasons, agile projects tend to avoid MultiSite technology. This is why the ClearCase Remote Client (CCRC) technology was developed; it allows distributed development based off a single server. The first releases of the CCRC had limited functionality; however, as of the version 7.0 release, it will have sufficient functionality for the majority of distributed projects. It should therefore be the recommended way of working for distributed agile projects going forward. The screenshot in Figure 3 illustrates the ClearCase Remote Client working in an Eclipse environment.
Figure 3: ClearCase Remote Client working in an Eclipse environment
- Avoid over-customization of ClearQuest change control. Implement an open or customizable change request workflow. The IBM Rational ClearQuest tool can provide a very powerful and sophisticated change- and defect-tracking facility. Although a number of agile projects using ClearCase have avoided using ClearQuest entirely, more and more projects are looking at ClearQuest and also UCM to see if it can be applied to help them meet their organization's compliance and regulatory requirements. Certainly ClearQuest can have a place in automating the capture, prioritization, and allocation of a typical change request and feature backlog, as I mentioned at the beginning of this article. However, too much process enforcement or micro-management can make it time-intensive for developers to start work on new change tasks. If not done with care, this can significantly slow down the overall development process and reduce the productivity of the agile project. To avoid this, agile projects typically implement a lightweight or customizable ClearQuest change request workflow. This is particularly relevant where ClearQuest is being used across an organization. Some projects in that organization might require more process control and management, a lot of which can be embedded in the ClearQuest tool. However, agile projects might not need or desire the same amount of process control and management. Organizations working with such environments have been successful by allowing the change request workflow to be configurable by each project. However, such an implementation requires detailed knowledge of both the ClearQuest tool and the requirements of different project processes and should not be undertaken lightly.
In this article, I have discussed the concept of agile SCM and best practices regarding how it can be implemented using IBM Rational ClearCase and IBM Rational ClearQuest. Hopefully, this discussion has convinced you that a suitable process can be found and implemented to support agile projects. It is worth noting that the implementation of an Agile SCM environment is not something that should be restricted to just agile projects. There are many projects that do not consider themselves as agile, but yet have similar SCM requirements. These tend to be smaller IS/IT projects where the configuration of a similar environment would be very practical. But it's worth noting that even larger projects could learn something by implementing a more lightweight and well-designed SCM process such as the one described here. In particular, the practices of build automation (including compilation and testing), pre-built binary staging, and composite releasing could be adopted by any project.
There is no reason why an enterprise SCM toolset, such as the IBM Rational toolset, cannot be used to support the implementation of agile development methods. The key is to define and implement an agile SCM process that focuses on supporting, rather than restricting, the agile team. It can be a tricky exercise to find the right governance model for such a team, but a general recommendation would be to start with a more open process, only implementing restriction where necessary. Feedback is also an essential part of agile development methods. One of the ways that SCM can help with this feedback mechanism is via an automated build and testing (and deployment) process. It is therefore recommended that you invest a significant amount of time looking at this aspect of your overall process.
1 For a discussion of the relative merits and successes of agile versus traditional development methods, see Barry Boehm and Richard Turner's excellent book, Balancing Agility and Discipline: A Guide for the Perplexed: Addison Wesley 2004. Alternatively, for up-to date discussions and case studies on agile development methods, you can visit and subscribe to The Agile Journal (http://www.agilejournal.com).
2 Stephen P. Berczuk and Brad Appleton, Software Configuration Management Patterns. Effective Teamwork, Practical Integration. Addison Wesley 2003. See also Brad Appleton et al., Streamed Lines: Branching Patterns for Parallel Software Development. PLoP Conference: 1998. http://www.cmcrossroads.com/bradapp/acme/branching/
3 See Appleton, 1998, Op. cit.
4 For more information on how to set up an automated build environment for agile projects, see Kevin A. Lee, IBM Rational ClearCase, Ant and CruiseControl. The Java Developers Guide to Accelerating and Automating the build process. Addison Wesley 2006.
Kevin A. Lee has more than a decade of experience in implementing software build and release management practices on projects of various sizes. He joined Rational Software, UK in 2000 as a technical field representative, and helps customers successfully deploy and adopt the IBM Rational Software Development Platform. In addition to delivering presentations at IBM Rational user conferences worldwide and writing articles for IBM developerWorks, he contributes to related open-source projects such as Apache Ant and CruiseControl. In his previous positions at large telecom organizations, he deployed the Rational Software Configuration Management (SCM) toolset on multisite enterprise projects. He holds a B.S. in computer science from the University of East Anglia.