Recently, the phenomenon of switching back from microservice to monolith has increased in frequency, leading to intense debate in the industry. In this paper, we conduct a multivocal literature review to investigate reasoning and key aspects to pay attention to when switching back and analyze other practitioners’ opinions. The results show four cases of switching back from microservice to monolith: Istio control plane, Amazon Prime Video monitoring service, Segment, and InVision. The five main reasons that led to switching back are cost, complexity, scalability, performance, and organization. During the switching back process, six key aspects need to be addressed: (1) stopping the development of more services, (2) consolidating and testing paths, (3) unifying data storage, (4) implementing the message bus principle, (5) giving up diverse techniques, and (6) learning to use modular design principles. As to the practitioners’ opinions, they had mixed views about the switching back phenomenon. However, most thought that switching back required consideration of the actual system situation and principles. These results pave the way for further research and guide researchers and companies through the process of switching back from microservice to monolith.

Recently, modular monolith architecture has attracted the attention of practitioners, as Google proposed a "Service Weaver" framework to enable developers to write applications as modular monolithic and deploy them as a set of microservices. Google considered it a framework with 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.

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.