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Modularization strategies

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Modularization Strategies Deep Dive

Overview

Modularization improves build performance and ownership clarity when boundaries reflect business capabilities and dependency direction rules.

Core Concepts

  • split by feature ownership and change cadence
  • keep API surface explicit and minimal
  • avoid cyclic dependencies between modules
  • enforce contracts through architecture checks

Layer Responsibilities

  • App shell module:
  • startup wiring, global navigation graph, DI root
  • Core/platform modules:
  • shared infrastructure (network, logging, analytics)
  • Feature modules:
  • feature UI orchestration and local domain policies
  • Shared contract modules:
  • interfaces/events used across features

Data Flow

  1. Feature UI triggers action in feature ViewModel.
  2. ViewModel calls feature/domain use case.
  3. Use case uses contracts from shared/core modules.
  4. Data module implementation executes and returns domain results.
  5. Feature maps domain output to UI state.

Internal Architecture

Common module patterns:

  • vertical feature slices (:feature:checkout, :feature:profile)
  • horizontal platform modules (:core:network, :core:database)
  • contract-only modules for inter-feature communication

Tooling to keep boundaries healthy:

  • dependency graph visualization
  • forbidden dependency lint rules
  • API/ABI boundary checks in CI

Code Examples

// In :feature:orders-api
interface OrdersNavigator {
    fun openOrderDetails(orderId: String)
}

// In :feature:orders-impl
class OrdersNavigatorImpl(
    private val navController: NavController
) : OrdersNavigator {
    override fun openOrderDetails(orderId: String) {
        navController.navigate("orders/$orderId")
    }
}

Common Interview Questions

  • Q: When does modularization become over-engineering? A: Answer by defining boundaries and ownership first, then place business rules in the correct layer, and finish with testability and change-resilience tradeoffs.
  • Q: How do you handle shared code without creating a "god core" module? A: Answer by defining boundaries and ownership first, then place business rules in the correct layer, and finish with testability and change-resilience tradeoffs.
  • Q: API vs implementation dependency - what changes in build behavior? A: Answer by defining boundaries and ownership first, then place business rules in the correct layer, and finish with testability and change-resilience tradeoffs.
  • Q: How do teams migrate a monolith incrementally? A: Answer by defining boundaries and ownership first, then place business rules in the correct layer, and finish with testability and change-resilience tradeoffs.

Production Considerations

  • start with a few high-value boundaries, then iterate
  • assign explicit owners per module
  • define deprecation/migration policy for shared APIs
  • measure build and integration metrics continuously

Scalability Tradeoffs

  • Pros:
  • parallel team delivery and safer refactoring
  • improved incremental build performance
  • Cons:
  • coordination overhead for shared contracts
  • potential over-fragmentation and dependency friction

Senior-Level Insights

Senior engineers should connect module boundaries to team topology. Good architecture reduces cross-team blocking and makes ownership visible.