The Commit Stage
A new instance of your deployment pipeline is created upon every check-in and, if the first stage passes, results in the creation of a release candidate. The aim of the first stage in the pipeline is to eliminate builds that are unfit for production and signal the team that the application is broken as quickly as possible. We want to expend a minimum of time and effort on a version of the application that is obviously broken. So, when a developer commits a change to the version control system, we want to evaluate the latest version of the application quickly. The developer who checked in then waits for the results before moving on to the next task.
There are a few things we want to do as part of our commit stage. Typically, these tasks are run as a set of jobs on a build grid (a facility provided by most CI servers) so the stage completes in a reasonable length of time. The commit stage should ideally take less than five minutes to run, and certainly no more than ten minutes. The commit stage typically includes the following steps:
- Compile the code (if necessary).
- Run a set of commit tests.
- Create binaries for use by later stages.
- Perform analysis of the code to check its health.
- Prepare artifacts, such as test databases, for use by later stages.
The first step is to compile the latest version of the source code and notify the developers who committed changes since the last successful check-in if there is an error in compilation. If this step fails, we can fail the commit stage immediately and eliminate this instance of the pipeline from further consideration.
Next, a suite of tests is run, optimized to execute very quickly. We refer to this suite of tests as commit stage tests rather than unit tests because, although the vast majority of them are indeed unit tests, it is useful to include a small selection of tests of other types at this stage in order to get a higher level of confidence that the application is really working if the commit stage passes. These are the same tests that developers run before they check in their code (or, if they have the facility to do so, through a pretested commit on the build grid).
Begin the design of your commit test suite by running all unit tests. Later, as you learn more about what types of failure are common in acceptance test runs and other later stages in the pipeline, you should add specific tests to your commit test suite to try and find them early on. This is an ongoing process optimization that is important if you are to avoid the higher costs of finding and fixing bugs in later pipeline stages.
Establishing that your code compiles and passes tests is great, but it doesn't tell you a lot about the nonfunctional characteristics of your application. Testing nonfunctional characteristics such as capacity can be hard, but you can run analysis tools giving you feedback on such characteristics of your code base as test coverage, maintainability, and security breaches. Failure of your code to meet preset thresholds for these metrics should fail the commit stage the same way that a failing test does. Useful metrics include:
- Test coverage (if your commit tests only cover 5% of your codebase, they're pretty useless)
- Amount of duplicated code
- Cyclomatic complexity
- Afferent and efferent coupling
- Number of warnings
- Code style
The final step in the commit stage, following successful execution of everything up to this point, is the creation of a deployable assembly of your code ready for deployment into any subsequent environment. This, too, must succeed for the commit stage to be considered a success as a whole. Treating the creation of the executable code as a success criteria in its own right is a simple way of ensuring that our build process itself is also under constant evaluation and review by our continuous integration system.
Commit Stage Best Practices
Most of the practices described in Chapter 3, "Continuous Integration," apply to the commit stage. Developers are expected to wait until the commit stage of the deployment pipeline succeeds. If it fails, they should either quickly fix the problem, or back their changes out from version control. In the ideal world—a world of infinite processor power and unlimited network bandwidth—we would like our developers to wait for all tests to pass, even the manual ones, so that they could fix any problem immediately. In reality, this is not practical, as the later stages in the deployment pipeline (automated acceptance testing, capacity testing, and manual acceptance testing) are lengthy activities. This is the reason for pipelining your test process—it's important to get feedback as quickly as possible, when problems are cheap to fix, but not at the expense of getting more comprehensive feedback when it becomes available.
Passing the commit stage is an important milestone in the journey of a release candidate. It is a gate in our process that, once passed, frees developers to move on to their next task. However, they retain a responsibility to monitor the progress of the later stages too. Fixing broken builds remains the top priority for the development team even when those breakages occur in the later stages of the pipeline. We are gambling on success—but are ready to pay our technical debts should our gamble fail.
If you only implement a commit stage in your development process, it usually represents an enormous step forward in the reliability and quality of the output of your teams. However, there are several more stages necessary to complete what we consider to be a minimal deployment pipeline.