How do microservices evolve? An empirical analysis of changes in open-source microservice repositories

Context. Microservice architectures are an emergent service-oriented paradigm widely used in industry to develop and deploy scalable software systems. The underlying idea is to design highly independent services that implement small units of functionality and can interact with each other through lightweight interfaces. Objective. Even though microservices are often used with success, their design and maintenance pose novel challenges to software engineers. In particular, it is questionable whether the intended independence of microservices can actually be achieved in practice. Method. So, it is important to understand how and why microservices evolve during a system’s life-cycle, for instance, to scope refactorings and improvements of a system’s architecture or to develop supporting tools. To provide insights into how microservices evolve, we report a large-scale empirical study on the (co-)evolution of microservices in 11 open-source systems, involving quantitative and qualitative analyses of 7,319 commits. Findings. Our quantitative results show that there are recurring patterns of (co-)evolution across all systems, for instance, “shotgun surgery” commits and microservices that are largely independent, evolve in tuples, or are evolved in almost all changes. We refine our results by analyzing service-evolving commits qualitatively to explore the (in-)dependence of microservices and the causes for their specific evolution. Conclusion. The contributions in this article provide an understanding for practitioners and researchers on how microservices evolve in what way, and how microservice-based systems may be improved.