Module Boundaries

The Problem

In a monolithic application, it’s easy for code to become tangled. Without clear boundaries, dependencies grow organically and the system becomes difficult to change.

Module boundaries help prevent this by establishing clear contracts between parts of the system.

The Solution

Define modules based on business capabilities, not technical layers. Each module should:

  • Own its data
  • Expose a clear API
  • Hide its implementation details
  • Communicate with other modules through well-defined contracts

Implementation

There are several ways to enforce module boundaries in your codebase:

  1. Separate projects/assemblies - Use your language’s module system
  2. Architecture tests - Automated tests that verify dependencies
  3. Code review - Manual verification of boundary compliance
  4. Static analysis - Tools that check for boundary violations