Refactoring Microservices to Microservices in Support of Evolutionary Design

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Evolutionary design</i> is a widely accepted practice for defining microservice boundaries. It is performed through a sequence of incremental refactoring tasks (we call it <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">“microservice refactoring”</i>), each restructuring only part of a microservice system (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a.k.a., refactoring part</i>) into well-defined services for improving the architecture in a controlled manner. Despite its popularity in practice, microservice refactoring suffers from insufficient methodological support. While there are numerous studies addressing similar software design tasks, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i>.<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</i>., software remodularization and microservitization, their approaches prove inadequate when applied to microservice refactoring. Our analysis reveals that their approaches may even degrade the entire architecture in microservice refactoring, as they only optimize the refactoring part in such applications, but neglect the relationships between the refactoring part and the remaining system. As the first response to the need, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Micro2Micro</i> is proposed to re-partition the refactoring part while optimizing three quality objectives including the interdependence between the refactoring and non-refactoring parts. In addition, it allows architects to intervene in the decision-making process by interactively incorporating their knowledge into the iterative search for optimal refactoring solutions. An empirical study on 13 open-source projects of different sizes shows that the solutions from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Micro2Micro</i> perform well and exhibit quality improvement with an average up to 45% to the original architecture. Users of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Micro2Micro</i> found the suggested solutions highly satisfactory. They acknowledge the advantages in terms of infusing human intelligence into decisions, providing immediate quality feedback, and quick exploration capability.