In-depth Comparison of Bazel and Gradle Build Systems for Android

The article, authored by the AppInfra‑Build team, analyzes Gradle and Bazel from a build‑system perspective, focusing on their design concepts, advantages, and disadvantages, especially for Android builds in large monorepo environments.

Core Concepts of Build Systems

A build system automates the generation of targets (libraries, executables, scripts) from source code. Major systems include CMake, Maven, Gradle, and Bazel. Both Bazel and Gradle support multiple languages and extensibility via plugins (Gradle) or rules (Bazel).

Key elements of a mature build system are:

Core scheduling mechanism (engine)

Build rule DSL (Gradle uses Groovy/Kotlin; Bazel uses Starlark)

Cache system

Dependency management

Extensibility (plugins/rules)

Deep Comparison

Design Philosophy

Bazel follows an artifact‑based (product‑driven) model, automatically inferring dependencies from produced artifacts, while Gradle is task‑based, requiring explicit task dependencies.

Example table:

System

Philosophy

Explanation

Bazel

产物驱动型

Declare what artifacts are needed; Bazel resolves implicit dependencies between actions.

Gradle

任务驱动型

Define tasks with explicit dependsOn relationships.

Concurrency

Bazel’s artifact‑driven design can automatically detect file overlaps and schedule tasks concurrently, offering higher concurrency. Gradle uses a Worker API to achieve similar concurrency when tasks share resources.

Incremental Build

Both systems use a daemon process and virtual file system (VFS) for change detection. Bazel’s DAG pruning enables minimal rebuilds, while Gradle relies on incremental tasks, daemon, VFS, and remote cache.

└── java
└── com
├── A.java
├── B.java
├── C.java
└── util
├── D.java
├── E.java
└── F.java

Configuration Phase

Gradle’s configuration phase generates the DAG for execution, whereas Bazel’s DAG spans the entire lifecycle, allowing cache reuse during analysis.

Gradle introduced a Configuration Cache to serialize the DAG when configurations do not change, but it remains a workaround.

Other Core Capabilities

Distributed compilation is a core feature of Bazel but absent in Gradle. Dependency management is stronger in Gradle (Maven‑based) than in Bazel, which originally lacked remote dependencies.

Android Build Comparison

Performance depends not only on the build system but also on tooling such as Android Gradle Plugin (AGP) and Bazel’s rules_android. AGP is mature and feature‑rich, while rules_android is less complete.

Kotlin Gradle Plugin (KGP) outperforms Bazel’s rules_kotlin. Gradle provides incremental tasks for Java compilation, giving it an edge in many scenarios.

Benchmark

A real‑world benchmark on an 80‑module Android project (Feishu Docs) compared Gradle 6.7.1 + AGP 4.1.0 against Bazel 6.2.1. Results:

Scenario

Gradle

Bazel

Explanation

NoChange

20 s

0.222 s

VFS + DAG pruning

Bottom‑module ABI Change

35 s

95.8 s

Gradle incremental tasks excel

Bottom‑module Non‑ABI Change

35 s

18.5 s

Bazel’s analysis advantage

Top‑module ABI Change

30 s

31.5 s

Similar to bottom‑module ABI

Top‑module Non‑ABI Change

30 s

16.6 s

Similar to bottom‑module Non‑ABI

Full‑build without cache showed Bazel taking 969 s (optimized to 248 s after PRs), while Gradle took 120 s.

Ecosystem

Android Studio integrates tightly with Gradle/AGP, whereas Bazel support relies on community effort and lags behind. Bazel’s Android ecosystem is still maturing, with a roadmap to rewrite Android rules in Starlark.

Conclusions and Recommendations

For ultra‑large monorepos, Bazel offers higher theoretical performance limits, but its ecosystem and tooling are less mature. Gradle, with its robust ecosystem and incremental task support, remains practical for most Android projects, especially when optimized.

The BuildInfra team plans to continue investing in Bazel research while leveraging its design insights to improve Gradle workflows.