SOLID & Design Patterns Interview Question #109

What is the Modular Monolith pattern?

Architectural Patterns, Application Boundaries & Distributed Design Patterns Senior Advanced

Quick Interview Answer

A Modular Monolith is deployed as one application but internally divided into strongly separated business modules. Each module owns its logic and should expose deliberate contracts rather than allowing unrestricted access to its internals.

Detailed Explanation

A Modular Monolith is deployed as one application but internally divided into strongly separated business modules. Each module owns its logic and should expose deliberate contracts rather than allowing unrestricted access to its internals.

It can provide many modularity benefits without the network, deployment, and operational complexity of microservices. The quality of boundaries matters more than simply creating multiple folders or projects.

Code Example

Application
  |- Sales Module
  |- Billing Module
  |- Inventory Module
  |- Support Module

// One deployment, explicit module boundaries.