CI/CD Pipelines Evolution and Restructuring: A Qualitative and Quantitative Study

Continuous Integration and Delivery (CI/CD) pipelines entail the build process automation on dedicated machines, and have been demonstrated to produce several advantages including early defect discovery, increased productivity, and faster release cycles. The effectiveness of CI/CD may depend on the extent to which such pipelines are properly maintained to cope with the system and its underlying technology evolution, as well as to limit bad practices. This paper reports the results of a study combining a qualitative and quantitative evaluation on CI/CD pipeline restructuring actions. First, by manually analyzing and coding 615 pipeline configuration change commits, we have crafted a taxonomy of 34 CI/CD pipeline restructuring actions, either improving extra-functional properties or changing the pipeline's behavior. Based on such actions, we have developed a metric extractor for Travis-CI pipelines, which extracts 16 indicators of how a pipeline evolves. The analysis of the pipeline evolution for 4,644 projects using Travis-CI and developed in 8 programming languages shows how some pipeline components, such as jobs and steps tend to change more often than others, but also the Docker adoption by the projects increases over time.