3x3: iOS Build Speed and Stability

LinkedIn's iOS team set an audacious goal: ship to production three times daily, with just three hours from commit to release. Here's how they actually pulled it off.

In 2016, LinkedIn's mobile engineering team documented their journey to achieve a 3x3 release cadence for their Voyager app. They started with 4.5 hour build times and needed to get under three hours while maintaining stability.

Key Takeaways

• Modular refactoring cut debug builds 50% and release builds from 2 hours to 35 minutes
• KIF framework optimizations achieved 5-10x faster UI testing, dropping from 2.5 hours to 20 minutes
• Distributed building across 10 machines reduced total time to 45 minutes
• Consolidated testing on one machine with 5 parallel simulators improved stability from 0% to 96%
• Key insight: 10 machines at 95% reliability each equals only 60% system reliability

The distributed testing approach initially made things worse before they discovered an elegant solution involving simulator process limits.