Kotlin Multimodule Android Architecture for Large-Scale Applications

As Android applications expand in size, a single Gradle module becomes more difficult to manage due to increased build times, tightly coupled dependencies, and accidental inter-feature relationships. A multimodule architecture addresses these issues by dividing the application into independently managed modules while maintaining clear dependency boundaries.

A large application can be structured with modules such as core, domain, and feature. The core module contains shared code like common, network, and database functionalities. Feature modules like auth, orders, and profile can be built as feature:auth, feature:orders, feature:profile, and feature:payments. Each feature adheres to Clean Architecture by separating presentation, domain, and data layers within the feature module.

Gradle configuration includes declaring modules in the settings.gradle.kts file, with each feature module depending on the necessary shared modules. Features should consume shared functionality through implementation dependencies, favoring implementation over api unless a dependency must be exposed to consumers. Dependency direction should follow a tree-like structure from app to features, domain, and then core.

To maintain a healthy dependency graph, avoid direct feature-to-feature dependencies. Instead, define abstractions, such as interface UserProvider { suspend fun getUser(): User }, and have features depend on these interfaces rather than implementations. This promotes loose coupling between modules.

Shared modules such as core:common, core:network, core:database, and core:designsystem can be useful for providing common functionalities across multiple features. It is crucial not to create a monolithic core module containing every shared dependency, as this can lead to increased build complexity. Incremental compilation benefits from multimodule projects, as changes are isolated to specific modules.

Each module can have independent tests, including unit tests, repository tests, and UI tests, making it easier to validate features without always building the entire application.

Convention plugins help centralize common settings like Android, Kotlin, Compose, testing, and publishing configuration. This reduces the need for duplicating configuration throughout the repository. Common mistakes to avoid include creating one enormous core module, establishing feature-to-feature dependency chains, excessively creating modules, exposing dependencies unnecessarily with api, and putting business logic into build configuration.

In conclusion, a multimodule architecture is not about maximizing the number of modules but about creating boundaries that allow independent building, testing, and changing of application parts. For large Kotlin Android applications, combining feature modules, dependency inversion, focused core modules, and convention plugins offers a scalable foundation.