Breaking up the App Module Monolith: The Story of Robinhood's Android App

Robinhood's Android app hit a wall: 100k+ dex count, skyrocketing build times, and features breaking each other. Sound familiar?

Jin Cao from Robinhood Engineering shares their journey from a 2-module monolith to 30+ independent feature modules. This is the story of how rapid growth turned their clean codebase into a tightly coupled mess, and what they did about it.

Key Takeaways

• Started with just 2 modules (librobinhood and app), everything accessible to everything
• Bottom nav bar reuse caused silent breakage across unrelated features
• Extracted 30+ modules with strict rule: no feature depends on another feature
• Created lib-navigation for cross-feature routing without explicit dependencies
• Duplicated code when features only looked similar, avoiding over-abstraction

The team discovered they could create custom build flavors that compile only one feature module at a time, dramatically speeding up development cycles.