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Comparing Bazel, Lerna, Nx, and Pants

Kenny DuMez
Kenny DuMez
Graphite software engineer

Monorepos, or monolithic repositories, are a source control strategy where multiple projects reside in a single repository. They can simplify dependency management, streamline code reuse, and enhance collaboration across large teams. However, managing a monorepo can become complex, especially as the size and scope of projects grow. This is where monorepo management tools come into play. These tools help manage builds, testing, and dependencies efficiently in a monorepo setup. Here’s an in-depth guide on some of the best monorepo tools available for software developers.

Bazel is an open-source build tool developed by Google, designed to support large codebases across multiple repositories. It is particularly well-suited for monorepo environments.

Key features:

  • Incremental builds: Bazel builds only the parts of your project that have changed, rather than the entire project. This is done by analyzing the dependencies defined in your build scripts.
  • Parallel execution: It can run multiple build actions in parallel, speeding up the build process significantly.
  • Extensibility: Supports custom build tasks using its extension language, Starlark, which is a dialect of Python.

How it works: Bazel uses a set of BUILD files to describe the project's structure and dependencies. These files contain Python-like scripts that tell Bazel how to build different parts of the project. When you run a build, Bazel computes a dependency graph from these descriptions and executes the build actions in a sandboxed environment.

Lerna is a tool that optimizes the workflow around managing multi-package repositories with Git and npm. It's particularly popular in the JavaScript community.

Key features:

  • Automated version management: Lerna can automatically determine which versions of packages need to be bumped based on your commits.
  • Independent vs. fixed modes: Allows you to manage versions of packages either independently or fixed (synchronized version numbers across all packages).

How it works: Lerna splits your monorepo into multiple npm packages, allowing you to update, version, and deploy them independently. It uses npm or Yarn to handle package dependencies.

Nx is a powerful build framework for modern web applications and is tailored for Angular but also supports many other JavaScript frameworks like React and Node.js.

Key features:

  • Integrated testing and linting tools: Provides out-of-the-box support for Jest, Cypress, ESLint, and more.
  • Computation caching: Nx caches the outputs of commands and tasks, which significantly reduces the build time by reusing computation from previous runs.

How it works: Nx uses advanced code analysis to understand your application structure and its dependencies. When a change is made, Nx will only retest and rebuild the necessary parts of the application instead of the entire thing.

Pants is another build system that excels in monorepo environments, especially for large codebases in Python, Java, and Scala.

Key features:

  • Fine-grained dependency management: Pants works at the file level rather than the package level, making its dependency management highly precise.
  • Concurrent builds: Similar to Bazel, Pants supports parallel builds and tests, which are crucial for large projects.

How it works: Pants uses BUILD files to create a directed acyclic graph (DAG) of targets, which are the basic units of work. It then executes tasks on these targets based on the dependencies defined.

Selecting the right monorepo tool depends on your specific needs:

  • Bazel is ideal for very large codebases with robust infrastructure and a need for highly scalable builds.
  • Lerna is best suited for JavaScript developers managing multiple packages within a single repo.
  • Nx offers a great balance for web application developers who need fast, reliable builds and are using modern JavaScript frameworks.
  • Pants is optimal for projects primarily using Python, Java, or Scala, offering precise build options.

These tools collectively cover a wide array of development scenarios, ensuring efficient management of your monorepo regardless of scale or technology stack.

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