Migrating Airbnb’s JVM Monorepo to Bazel

Airbnb completed a 4.5-year migration of their JVM monorepo (tens of millions of lines of Java, Kotlin, and Scala) from Gradle to Bazel.

• •Build CSAT improved from 38% to 68%, with 3–5x faster local builds, 2–3x faster IntelliJ syncs, and 2–3x faster dev environment deploys
• •Bazel's remote build execution (RBE) scaled to thousands of parallel actions, replacing inefficient machine-sharding heuristics used with Gradle
• •Sandboxing and hermetic builds eliminated reliability issues like race conditions caused by Gradle tasks accessing the shared file system
• •An automated build file generator (inspired by Gazelle) was built to maintain co-existing Gradle and Bazel build graphs without burdening developers
• •The migration resulted in >10x more fine-grained Bazel targets than Gradle projects, enabling more parallelism and less cache invalidation