  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.
