From Monolith to Microservices: A Classification of Refactoring Approaches

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.

Microservices Migration in Industry: Intentions, Strategies, and Challenges

“…For these systems we can observe a significant overlap with using the existing system's structure as a basis (Table III). Refactoring approaches described in academic literature that partly offer tool support [26] were not considered by any of our interviewees. When asked directly, they were not aware of any such tools (P6, P14) or convinced that there is no way to automate it (P2, P12).…”

A multi-model based microservices identification approach

“…As per Section 3.2, coupling and cohesion are important aspects to consider when assessing the quality of microservices. To this end, we rely on the work of [15] that quantifies both aspects using four metrics, Afferent Coupling (AC), Efferent Coupling (EC), Instability (I), and Relational Cohesion (RC) (Table 12), with focus on AC and RC. Since these metrics refer to classes and class packages, we mapped them onto concepts relevant and applicable to our work.…”

“…The system also includes two core modules, dependency analysis and microservice extraction. The first parses the XML-based BP to extract all execution paths between any couple of activities < a i , a j > and their respective artefact/attribute exchange, as well, and takes the BP's OWL domain ontology developed under Protégé 5.5 15 , as input. Note that artefacts/attributes will be associated with criticality values as per Section 3.4.…”

Towards a Process for Migrating Legacy Systems into Microservice Architectural Style

“…Therefore, the proposed process in this paper has the goal broader. Despite of existing secondary studies such as [Di Francesco et al 2019, Fritzsch et al 2018, Ponce et al 2019, Francesco et al 2017, which map primary studies describing characteristics of the migration, they do not describe a consolidated and comprehensive process. So, to the best of our knowledge, our study is the first one that presents recommendations and/or guidelines on how to perform the migration process.…”