Sajangnim Plus App Architecture Migration Case Study

Kakaopay migrated the architecture of the Sajangnim Plus app from its existing RIBs and TCA to a custom MVVM approach in order to improve code readability and boost development productivity.

This migration was carried out based on the following two core goals.

• Writing readable code: Reducing excessive protocols and object separation to improve code readability and lower the barrier to entry for development
• Service-tailored Clean Architecture: Designing a structure optimized for the Sajangnim Plus environment

On the structural side, the team referenced Android's per-layer modularization approach, but to reduce iOS complexity, they adopted a method of separating layers into folders within a module rather than across modules. This decision prioritized maintainability and project complexity management over the benefits of build time.

They also reduced the enforcement of the Domain Layer to secure flexibility. When business logic is not complex, UseCase is optionally introduced, and a vertical tree structure was designed allowing the Presentation Layer to depend directly on the Data Layer, maximizing development efficiency.