The Modular Monolith - Why It's Better Than Microservices

Microservices have become a popular architectural style for building applications, breaking them into small, discrete services that communicate through APIs. However, while microservices offer some advantages, the modular monolith is emerging as an alternative worth considering. In this article I'll outline the key benefits modular monoliths have over microservices:

1. Simplicity and Ease of Development

With microservices, an application is split across dozens or hundreds of services. That's dozens of codebases to manage, Docker files to maintain, CI/CD pipelines to set up, infrastructure, and networking challenges to tackle. The burden put on developers and operations teams is immense. Modular monoliths on the other hand keep the entire codebase in one place, with clear separations between modules. This drastically reduces complexity for developers. Changes can be made and tested faster, and deployment happens in one step.

2. Better Performance

Because all modules live in the same process in a modular monolith, calls between modules are fast in-memory function calls. With microservices there is significantly more networking overhead as services must communicate through protocols like HTTP/REST or messaging. This can get very chatty and introduce noticeable latency.

3. Transactional Integrity

Since a modular monolith runs as a single system, executing transactions that span modules is straightforward. With microservices complex distributed transactions are notoriously difficult to implement correctly. Keeping data consistent becomes error-prone and adds a lot of complexity.

1. Iterating and Refactoring

In a modular monolith refactoring modules and changing internal APIs means updating some code rather than managing breaking changes across service boundaries. Because services are decoupled, microservices versions and migrations become very painful. Agile development is much easier with a modular codebase.

In summary, while microservices come with allure - and are still the right choice in some cases - modular monoliths solve many of the same problems with a simpler, easier-to-manage architecture. If building a brand new application consider going modular first, and only break out microservices where a clear need to scale independently arises. This will reduce overhead and let you focus on delivering features quickly.