This is a response article to “Why don’t we use Continuous Integration?”  by user s1367762.
In his post , the author describes his own working experience in a small start-up company with mostly one developer at a time working on different small projects. As not all projects were using Continuous Integration, the author states a variety of reasons why not every software engineering company and project use it so far, based on his own experience.
This post discusses these various arguments that may prevent a company of implementing Continuous Integration for a software project. Generally, it is always a trade-off between software quality and resources.
The first point is that it may be difficult to make small incremental commits, when a change requires more time to make the whole software work again eventually. Commits in between would therefore break the build and the whole Continuous Integration pipeline.
I absolutely agree with that argument. When for example a new module is developed, at first the whole software may be broken. Not committing to the main line at least daily contradicts the basic rules of Continuous Integration; see for example  by Martin Fowler.
However, is that really a problem? From my personal business experience, it is very common and easy to implement a new feature in a new version control system branch, often referred to as a feature branch. This branch may have own Continuous Integration processes to ensure the quality, but in the first place this does not break the main build. When the feature is in a stable condition, the branch can be merged into the main product and be part of the general CI process. Martin Fowler’s blog post  describes this process in more detail.
The second point mentioned by s1367762, is that there may be code that is not really part of the software project, for example used only by a few customers for very special use cases. Therefore, it does not make sense to commit this code to the main line as suggested by Continuous Integration.
I absolutely understand this point. However, if there is some code that is not really part of the product, there is no need for Continuous Integration for these few special modules. From my point of view, CI can be implemented also when ignoring such modules.
I absolutely agree on this point, especially when dealing with GUI components, automating Tests is time-consuming and difficult. Furthermore, without having good code coverage Continuous Integration is less effective. However, it is better than no Continuous Integration at all. Also, this is clearly a trade-off between saving time not automating tests and final software quality.
Appropriate Timing, Direct Costs and Project ROI
In these three points the author states that it is more difficult to implement CI into an existing project that started without it. He furthermore describes the costs of learning to implement CI and operating build and test machines as expensive. Finally, he contends that implementing Continuous Integration is not worth the effort for short term project without long term maintenance.
All these points are completely understandable. To my mind, they all lead to one question for the project manager: How important is the quality of my project? If it is not a major requirement, for example if the software is being used only for a short period of time, Continuous Integration is not worth implementing.
In summary, s1367762 demonstrates well why Continuous Integration is not always a good idea in software projects. However, especially for the first point regarding commits frequency, it is easy to work around it by using feature branches without completely losing the idea of Continuous Integration. Furthermore, if there are modules that do not really belong to the project, they can be easily ignored for the CI approach. From my point of view, a partly implemented CI is much better than no CI at all.
Finally, everything depends on the management decision if maintaining quality by investing time and money is wanted for a project. The company I worked for never questioned the importance of quality, so Continuous Integration was implemented in sophisticated detail. However, if quality is not a major point in some projects, as s1367762 describes according to his business experience, it is absolutely reasonable not to implement Continuous Integration for some projects.
|s1367762, “Why don’t we use Continuous Integration? | SAPM: Course Blog,” [Online]. Available: https://blog.inf.ed.ac.uk/sapm/2014/02/14/why-dont-we-use-continuous-integration/ . [Accessed 27 2 2014].
|M. Fowler, “Continuous Integration,” 2006. [Online]. Available: http://www.martinfowler.com/articles/continuousIntegration.html . [Accessed 27 2 2014].
|M. Fowler, “FeatureBranch,” 2009. [Online]. Available: http://martinfowler.com/bliki/FeatureBranch.html . [Accessed 27 2 2014].