A lot of developers talk about modular architecture as if it’s simply a technical exercise.

  • Split the backend into services.
  • Split the frontend into modules.
  • Add lazy loading.
  • Done!

In reality, that’s usually where the problems begin.

At first, modularization looks simple. But once you start working on a large application with multiple developers, you quickly discover that modular architecture is mostly about boundaries, rules, and discipline.

Without clear conventions, documentation, and team-wide agreements, you’ll often end up with something worse than the original monolith: dozens of modules that are technically separated but tightly coupled in practice.

The code is no longer in one big application. It’s now scattered across many modules, services, and repositories. The complexity didn’t disappear. It just moved.

One lesson I learned is that separating frontend and backend is not enough.

A common mistake is creating feature modules while still allowing developers to import anything from anywhere. Teams often celebrate having multiple modules while a single change still ripples across half of the application.

A module is not defined by a folder, a module is defined by its boundaries.

If a team cannot remove, replace, or upgrade a module without affecting unrelated parts of the system, then the architecture is not truly modular.

Apply Modularity Everywhere

One habit I strongly recommend is applying modular thinking at every level of the codebase.

Not just features.

Not just services.

Everything.

Many teams create feature modules but continue building components that contain presentation logic, business rules, state management, and API communication all in the same place.

That’s not modularity. It’s just a smaller monolith.

For example:

  • Keep TypeScript logic separate from templates and styling responsibilities.
  • Avoid components that handle business logic, API communication, state management, and UI rendering at the same time.
  • Give each piece a single responsibility.
  • Define clear contracts between modules.
  • Document ownership and allowed dependencies.

The goal is to make every piece understandable, testable, and replaceable in isolation.

State Management Can Become a Hidden Monolith

State management is often where modular architectures silently fail.

If you’re using NgRx or another state management solution, avoid creating one giant global store that every feature depends on.

Instead:

  • Organize state by business domain.
  • Create independent slices with clear ownership.
  • Define strict boundaries between slices.
  • Prevent modules from directly modifying another module’s state.
  • Treat state contracts the same way you treat API contracts.

Otherwise, the state layer simply becomes a new monolith hiding inside a modular application.

Think Like Automotive Engineering

The best analogy I’ve found is a car.

A modern car is made of independent systems: navigation, climate control, braking, entertainment, sensors, and power management.

When a manufacturer upgrades the infotainment system, they don’t redesign the braking system.

Each part has clear responsibilities and well-defined interfaces.

Software modules should work the same way.

A module should be removable, replaceable, and scalable.

You should be able to remove one feature and replace it with a completely different implementation without forcing changes across the entire application.

That’s when modularity becomes more than a folder structure.

That’s when it becomes architecture.