Scale Rust Projects Efficiently With Bazel Build System

  • 25/9/2023
  • 2-minute read

Large Rust monorepos often rebuild too much and overwhelm local machines. Bazel’s dependency graph, remote caching, and reproducible builds address these pain points when paired with rules_rust.

Prerequisites

  • Bazelisk or Bazel ≥ 6.0 installed.
  • Rust toolchain managed via rustup or rules_rust toolchains.

Minimal Setup

WORKSPACE.bazel:

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

http_archive(
    name = "rules_rust",
    sha256 = "<latest-sha>",
    urls = ["https://github.com/bazelbuild/rules_rust/releases/download/<version>/rules_rust-<version>.tar.gz"],
)

load("@rules_rust//rust:repositories.bzl", "rust_repositories")

rust_repositories(
    edition = "2021",
)

BUILD.bazel:

load("@rules_rust//rust:defs.bzl", "rust_binary")

rust_binary(
    name = "app",
    srcs = ["main.rs"],
    deps = ["@rules_rust//examples/hello_lib"],
)

Scaling Techniques

  • Remote Cache/Execution: Configure .bazelrc with --remote_cache (GCS, S3, Buildbarn) and optionally --remote_executor for cluster builds.
  • Incremental Targets: Break crates into granular rust_library targets; Bazel recompiles only changed dependencies.
  • Toolchain Pinning: Use rust_register_toolchains to lock compiler versions and enable cross-compilation profiles.
  • Parallelism: bazel build //... --jobs=<cores> combined with remote execution saturates build clusters.

Debugging & Testing

  • Run bazel test //path:target for unit/integration tests; Bazel tracks flaky tests and caches results.
  • Inspect build graphs with bazel query --notool_deps --noimplicit_deps "deps(//path:target)" to understand rebuild hotspots.
  • Use bazel clean --expunge_async sparingly; prefer targeted cleans (bazel clean --async //path:target) to preserve cache efficacy.

Tips

  • Keep .cargo/config.toml in sync with Bazel toolchain flags if you also build with Cargo.
  • Monitor remote cache hit ratios—low values indicate missing dependencies or mismatched flags.
  • Harden CI with bazel build //... --config=ci to ensure reproducibility across developer machines and pipelines.
rustdevelopmentperformancetutorialdevops