Modular Monolith: Is This the Trend in Software Architecture?
Ruoyu Su, Xiaozhou Li
TL;DR
The paper investigates whether modular monoliths represent a meaningful trend that combines monolith development velocity with microservice scalability. It conducts a systematic grey literature review to define modular monolith, identify supporting frameworks, and catalog real-world cases. The findings show modular monolith structures organize software into loosely coupled modules with explicit boundaries and a single deployment unit, while remaining deployable as microservices if needed. Key frameworks identified are Service Weaver (Go), Spring Modulith, and Light-hybrid-4j, with Shopify, Appsmith, Gusto Time Tracking, and PlayTech as notable case studies. The work offers practical guidance for architecture decisions and suggests further research on migration pathways between modular monoliths and microservices.
Abstract
Recently modular monolith architecture has attracted the attention of practitioners, as Google proposed "Service Weaver" framework to enable developers to write applications as modular monolithic and deploy them as a set of microservices. Google considered it as a framework that has the best of both worlds and it seems to be a trend in software architecture. This paper aims to understand the definition of the modular monolith in industry and investigate frameworks and cases building modular monolith architecture. We conducted a systematic grey literature review, and the results show that modular monolith combines the advantages of monoliths with microservices. We found three frameworks and four cases of building modular monolith architecture. In general, the modular monolith is an alternative way to microservices, and it also could be a previous step before systems migrate to microservices.