In part 1 of this series, I described the essential elements of Continuous Integration within the context of agile development and briefly discussed the software options for a CI server. I explained that the building blocks of CI are a version control system and a build management tool. The former creates the foundation, by giving the CI process access to the latest copy of project source code. The latter then takes the source code and, in most scenarios, transforms it into the deployable binary artefact that represents the software application being developed.

It is useful to consider this transformational process as a series of steps or life-cycle phases. By analyzing our build in this conceptual way, we can better understand how to ‘bind’ or attach actions to each distinct life-cycle phase. Why is this important? Well, using this simple idea I can demonstrate how you can hardwire quality checks into to your CI process. Performing such checks, and publishing their results, means that we can really start to take advantage of the significant benefits CI can bring to your agile projects.

I actually prefer the term ‘quality gate’ as opposed to ‘quality check’ as it better fits the idea that you must pass through one gate before entering another. In each case, if we are unable to pass through the gate, we can choose to fail the build and our CI system should dispatch a notification to us. In addition, a good CI process will publish the metrics and ‘violations’ concerning each gate, so that they can be reviewed in detail after each build has occurred.

Build Life-Cycle Phases and Quality Gates

Phase 1 – Resolve component dependencies

Often our projects will have dependencies on other internal or third-party components. This is very common for example, in the Java or Ruby programming language worlds where the re-use of packaged binary artefacts (JAR’s for the former and Gem’s for the latter) is considered best practice. One key attribute of a released component is its version (e.g. 2.1.1) and it is here we can apply our first simple gate – ensure that we are using the correct versions of our dependent components.

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