From Monolith to Microservices: A Classification of Refactoring Approaches

TL;DR

This paper reviews and classifies 10 recent refactoring approaches for transitioning from monolithic to microservices architectures, providing a decision guide and highlighting their applicability, data needs, and tool support.

Contribution

It offers a systematic classification of existing refactoring strategies and visualizes their decision criteria for better guidance in microservices migration.

Findings

Most approaches are condition-specific

Significant input data requirements for some methods

Limited tool support for many strategies

Abstract

While the recently emerged Microservices architectural style is widely discussed in literature, it is difficult to find clear guidance on the process of refactoring legacy applications. The importance of the topic is underpinned by high costs and effort of a refactoring process which has several other implications, e.g. overall processes (DevOps) and team structure. Software architects facing this challenge are in need of selecting an appropriate strategy and refactoring technique. One of the most discussed aspects in this context is finding the right service granularity to fully leverage the advantages of a Microservices architecture. This study first discusses the notion of architectural refactoring and subsequently compares 10 existing refactoring approaches recently proposed in academic literature. The approaches are classified by the underlying decomposition technique and visually presented in the form of a decision guide for quick reference. The review yielded a variety of strategies to break down a monolithic application into independent services. With one exception, most approaches are only applicable under certain conditions. Further concerns are the significant amount of input data some approaches require as well as limited or prototypical tool support.