Understanding Monorepos: The Simplified Guide 📚

Introduction

Monorepos have been gaining popularity, especially in the web development community, as they offer a streamlined approach to managing multiple projects within a single repository. This post will explore what a monorepo is, its advantages over the traditional "polyrepo" approach, and a detailed look at various tools that can help you set up and manage monorepos effectively.

What is a Monorepo?

A monorepo (short for "monolithic repository") is a single code repository that contains multiple distinct projects with well-defined relationships between them. Unlike a polyrepo setup, where each project has its own repository, a monorepo centralizes everything, making it easier to share code and manage dependencies.

Monorepo ≠ Monolith
A common misconception is that a monorepo is a monolithic codebase, but this isn't true. Monorepos are modular and can be managed effectively to avoid the problems typically associated with monolithic architectures.

Monorepo vs. Polyrepo

To understand why monorepos can be advantageous, let's first examine the traditional polyrepo approach. In a polyrepo setup:

Each project has its own repository.
This setup promotes team autonomy but often leads to challenges in collaboration, code sharing, and consistency.

Monorepo vs. Polyrepo

Drawbacks of Polyrepos

Cumbersome Code Sharing
To share code across repositories, you might need a separate shared repo. This requires extra tooling, package publishing, and maintenance, which can lead to inconsistent versions across different projects.
Significant Code Duplication
Due to the hassle of setting up shared repositories, teams often re-implement common components, leading to wasted effort and higher maintenance costs.
Costly Cross-Repo Changes
Applying a bug fix across multiple repos is a tedious process, requiring separate environments, versioning coordination, and multiple deployments.
Inconsistent Tooling
Different projects often have their own tooling and build processes, creating mental overhead and increasing the chances of errors.

Advantages of Monorepos

Monorepos solve many of these problems by:

Eliminating Overhead for New Projects
You can use existing CI/CD setups without needing to publish packages or set up new build pipelines.
Atomic Commits Across Projects
Fix breaking changes across multiple projects in a single commit, ensuring that everything continues to work seamlessly.
One Version of Everything
With a single repository, there are no version conflicts, and every project uses the same version of dependencies.
Developer Mobility
Consistent build and testing setups allow developers to work across multiple projects easily, even if they are using different technologies.

Features of Monorepo Tools

To successfully manage a monorepo, the right tools are crucial. As your codebase grows, tools need to maintain performance, clarity, and manageability. Here are some key features to look for:

Key Features

Local Computation Caching: Stores and reuses the output of tasks locally, so you don’t have to build or test the same thing twice, saving time and resources.
Local Task Orchestration: Efficiently runs tasks in the correct order and can execute them in parallel, reducing the time taken to complete builds.
Distributed Computation Caching: Shares cache artifacts across different environments, preventing redundant builds/tests across CI agents.
Distributed Task Execution: Distributes tasks across multiple machines, maintaining the ease of running commands locally while speeding up processes.
Detecting Affected Projects: Automatically determines which projects might be affected by a change, ensuring that only those projects are built/tested, making processes efficient.
Workspace Analysis: Understands the project graph of the workspace without extra configuration, simplifying dependency management.
Dependency Graph Visualization: Visualizes relationships between projects/tasks with interactive features like search, filter, and highlight, helping developers understand connections and dependencies.
Source Code Sharing: Facilitates sharing discrete pieces of source code across projects within the same repo, reducing code duplication.
Consistent Tooling: Ensures a uniform experience across different technologies, meaning the same commands can be used for build, test, and deploy.
Code Generation: Supports generating code from templates, saving time on repetitive tasks.

Popular Monorepo Tools: A Comparison

Overview of Tools

Here’s a comparison of some popular tools used for managing monorepos:

Bazel: Known for robust distributed task execution, Bazel supports local and distributed computation caching. It’s ideal for projects with complex build pipelines, but has limited dependency graph support.
Gradle: Often used for Java and Kotlin projects, Gradle can manage complex builds and supports distributed computation caching, though setting up distributed task execution may require additional configuration.
Lage: Lightweight and simple, Lage is npm-focused and supports local computation caching. However, it lacks support for distributed task execution.
Lerna: A popular choice for JavaScript projects, Lerna works well when combined with Nx for enhanced features like distributed caching.
moon: Offers robust local caching and dependency graph visualization, but doesn’t support distributed task execution.
Nx: A versatile tool with strong support for JavaScript frameworks, Nx provides comprehensive dependency graph visualization, distributed task execution, and consistent tooling across projects.
Pants: Supports distributed task execution and caching, making it suitable for large-scale projects. Pants also excels in managing dependency graphs.
Rush: Focused on JavaScript projects, Rush supports distributed caching but has limited dependency graph support.
Turborepo: Easy to integrate with modern JavaScript frameworks, Turborepo supports local and distributed caching, though it doesn’t offer distributed task execution.

Tool Recommendations

Choosing the right monorepo tool depends on your specific use case. Here are some suggestions:

For Large Scale Projects
If you have a massive codebase with complex build pipelines, Bazel or Pants might be ideal. They offer robust distributed task execution and can handle projects with millions of lines of code.
For Web Development
Nx and Turborepo are popular among web developers due to their simplicity and integration with modern JavaScript frameworks like React, Angular, and Vue. Nx excels with TypeScript projects, providing built-in code generation and dependency graph visualization.
For Java and Kotlin Projects
Gradle is a reliable choice for JVM-based projects. It is extensible, has a strong plugin ecosystem, and can manage complex builds.
Lightweight Options
If you're looking for a simpler, npm-focused solution, Lage or Lerna might be suitable. They can be integrated with Nx to gain access to more advanced features like distributed caching.

Real-World Examples of Monorepos: Google and Meta

Google

Google is a leading technology company known for its extensive use of monorepos in managing its vast codebase. Their main monorepo, known as the "Google codebase," is reported to contain over 2 billion lines of code spread across various projects and services. To effectively manage their monorepo, Google developed a custom-built tool called Piper.

Piper provides features and capabilities that enable fast and efficient code sharing and collaboration within their organization. It streamlines code synchronization across different projects and enables efficient change tracking, allowing developers to work on multiple projects within the monorepo. Piper also integrates seamlessly with Google's code review processes, ensuring smooth and consistent development practices.

By centralizing their codebase in a monorepo, Google benefits from:

Streamlined Code Management: Easier handling of dependencies and project configurations.
Improved Collaboration and Knowledge Sharing: Teams can easily see and contribute to different projects, fostering a culture of shared ownership.
Increased Code Reuse: Engineers can leverage existing code to build and iterate on new features and products efficiently.

Meta (formerly Facebook)

Meta, one of the world's largest social networking companies, also utilizes a monorepo to manage its extensive codebase. With over 100 million lines of code, their monorepo encompasses numerous projects, libraries, and services. Meta employs a build tool called Buck, which is specifically designed to handle their monorepo.

Buck enables fast and efficient builds within the monorepo environment by incorporating advanced caching mechanisms to optimize build times. It avoids unnecessary recompilation of common dependencies, significantly speeding up the development process. Buck also integrates well with Meta's continuous integration (CI) and continuous delivery (CD) workflows, enabling rapid iterations and deployments.

By leveraging a monorepo, Meta benefits from:

Improved Code Sharing and Reuse: Common libraries and components are readily available across different projects, reducing duplication of effort.
Streamlined Collaboration: Development teams can work more closely, easily accessing and contributing to various parts of the codebase.
Increased Code Visibility and Maintainability: A single repository allows for better tracking of changes, making it easier to manage dependencies and maintain the codebase over time.

Resources

Here is a curated list of useful videos, podcasts, articles, and books to deepen your understanding of monorepos or to see the information from a different perspective.

Monorepo Videos & Podcasts

Here are some video and podcast recommendations about monorepos that will greatly complement what you’ve learned:

Monorepo Articles

Here is a curated list of articles about monorepos that will support your learning:

Monorepo Books

Here is a curated list of books about monorepos that are worth a read:

Effective React Development With Nx - Jack Hsu

A lot of successful organizations such as Google, Facebook, Microsoft—as well as large open-source projects such as Babel, Jest, and React—use the monorepo approach to software development. As you will see in this book, a monorepo approach can save developers from a great deal of headache and wasted time.

Learn How to Build Enterprise-Scale Angular Applications Which Are Maintainable in the Long Run - Manfred Steyer

Learn how to build enterprise-scale Angular applications that are maintainable over time. This book covers best practices for structuring your codebase and managing dependencies, making it a great resource for developers working in a monorepo environment.

Conclusion

Monorepos offer a compelling way to manage codebases with multiple projects, and choosing the right tools can greatly enhance your workflow. With benefits like consistent tooling, reduced code duplication, and ease of collaboration, monorepos can help teams work more effectively. Each tool has its strengths, so it’s essential to evaluate them based on your project’s needs.