How to show a modular monolith on a diagram in system design?

A modular monolith in a system design diagram is usually depicted as a single application divided into several logical modules or components within one block.

You can imagine a large rectangle — this is the monolith, inside which are smaller blocks, each responsible for a specific module (for example, authentication, business logic, data handling). Dependencies or interactions between modules are shown with arrows.

It is important to emphasize that all modules operate within a single process and are deployed together, unlike microservices. This diagram helps visually distinguish the boundaries of modules and their interactions within the monolith.