Modular monolith: is this the trend in software architecture?

However, several companies did not get the expected benefits from migrating to microservices, and fell into difficulty because of issues such as high cost and complexity of microservices [9].

Recently, the concept of "Modular Monolith" has attracted the attention of practitioners, as Google proposed the "Service Weaver" framework to enable developers to write applications as modular monolithic and deploy them as a set of microservices [3]. Google explains that it is a framework that has the best of both worlds: the development velocity of a monolith, with the scalability, security, and fault-tolerance of microservices [3].

The concept of modularization is not new knowledge, it has been proposed in the last century that modularization is a mechanism for improving the flexibility and comprehensibility of systems [8]. It differs from a monolithic system in that modularization divides the system into separate modules, and independent teams can work on each module so that it reduces product development time and has greater flexibility and comprehensibility [8].

The results show that Modular Monolith is a software architecture pattern that combines the advantages of monolith with microservices architecture. In this architecture, systems are organized into loosely coupled modules, each delineating well-defined boundaries and explicit dependencies on other modules.

We found three frameworks for building the modular monolith: Service Weaver, Spring Modulith, and Light-hybrid-4j.

Modular Monolith is a software architecture pattern that strategically combines the simplicity of a monolithic structure with the advantages of microservices.

The focus on business domains rather than technical layers, along with the vertical stacking of modules, enhances code organization and maintainability.

More importantly, Service Weaver has flexible scalability, it can easily scale applications horizontally or vertically on demand, whether as a monolithic application or a distributed microservice [S52].

Shopify is one of the largest Ruby on Rails codebases in existence, worked on for over a decade by more than a thousand developers [S12]. It was initially built as a monolith all the distinct functionalities were built into the same codebase with no boundaries between them. To better development, Shopify chose to change its architecture. Shopify originally considered microservices but finally chose modular monolith to balance the benefits of a single codebase with clear component boundaries. Therefore, Shopify is a great example that has used this approach as an alternative to microservice decomposition [S12][S30].