The Breaking Point
It was a Tuesday afternoon when our CI build failed for the 47th time that week due to a Dagger-related error. The error message? A cryptic wall of text pointing to an auto-generated class that no human should ever have to read.
I'd had enough.
Why Dagger Became a Problem
Don't get me wrong — Dagger is a powerful dependency injection framework. At compile time, it generates all the code needed to wire dependencies together. But with that power comes complexity:
- Annotation processing hell: Every
@Module,@Component,@Provides, and@Injectannotation adds to compile time. In our SDK with 200+ classes, builds were taking 4+ minutes just for Dagger code generation. - Cryptic error messages: When something goes wrong (and it will), Dagger throws errors that require a PhD in annotation processing to understand. "Cannot be provided without an @Inject constructor or an @Provides-annotated method" — but WHERE?
- Steep learning curve: Every new developer joining the team spent their first week just understanding our Dagger graph. Subcomponents, scopes, qualifiers, multibindings — the cognitive overhead was enormous.
- Testing nightmares: Setting up test modules with Dagger required almost as much boilerplate as the production code itself.
Enter Koin
Koin takes a fundamentally different approach. Instead of compile-time code generation, it uses a lightweight DSL to define dependencies at runtime:
val appModule = module {single { NetworkClient() }
single { UserRepository(get()) }
factory { LoginViewModel(get()) }
}
That's it. No annotations. No generated code. No component interfaces. Just clean, readable Kotlin.
The Migration Strategy
We couldn't migrate everything at once — the SDK had over 150 Dagger-managed dependencies. Here's how we did it in phases:
Phase 1: Leaf modules first — We started with modules that had no Dagger dependencies of their own. Analytics, logging, and utility modules were migrated first.
Phase 2: Bridge layer — We created a bridge that allowed Koin modules to consume Dagger-provided dependencies and vice versa. This was the trickiest part.
Phase 3: Core migration — Once 60% of modules were on Koin, we migrated the core networking and data layers.
Phase 4: Cleanup — Removed all Dagger dependencies, deleted generated code, and simplified the build.
The Results
After completing the migration:
- Build time dropped 40% — from 4.2 minutes to 2.5 minutes on average
- 326+ PRs were submitted during the migration over 3 months
- Onboarding time for new devs dropped from ~1 week to ~2 days
- Test setup code reduced by approximately 60%
- Zero runtime DI crashes in 6 months post-migration
Lessons Learned
- Don't migrate all at once — The bridge pattern saved us. We could ship incrementally without breaking anything.
- Write migration tests — For every module migrated, we wrote integration tests to verify the dependency graph was correct.
- Koin isn't perfect — Runtime DI means errors show up at runtime, not compile time. We mitigated this with
checkModules()in our test suite. - Team buy-in matters — I spent two weeks building a proof of concept and presenting it to the team before starting the actual migration.
Would I Do It Again?
Absolutely. Koin isn't just simpler — it's more Kotlin-idiomatic. It leverages Kotlin's language features instead of fighting against Java's annotation processing system. For our use case (an SDK with clear module boundaries), it was the perfect fit.
If you're considering the same migration, start small, measure everything, and don't let anyone tell you that "Dagger is the only professional choice." The best tool is the one that lets your team ship faster.