What is a Monorepo?

A monorepo is a software development strategy where the code for many different projects is stored in a single Git repository. This stands in contrast to a polyrepo (or multi-repo) approach, where each project has its own separate repository.

Companies like Google, Meta, and Microsoft are famous for using large-scale monorepos to manage their codebases. For these tech giants, a monorepo can contain the code for a vast array of projects, all in one place.

Here are some examples:

• The backend code for their main web applications.
• The frontend code for those same applications.
• Mobile applications for both iOS and Android.
• Shared libraries and services that are used across multiple projects.
• Internal tools and infrastructure code.

This allows them to manage dependencies, share code, and perform large-scale refactors with a high degree of confidence.

Monolith versus Monorepo

It's easy to confuse a monorepo with a monolith, but they are different concepts. Let's use an analogy to make the distinction clear.

Imagine a library:

• A monolith is like a single, giant encyclopedia. All the information is bound together in one massive book. To update a single entry, you have to reprint the entire encyclopedia. It's self-contained, but inflexible.

• A monorepo is like the entire library building. It contains many different books (projects) on various shelves (directories). You can have a shelf for fiction, another for science, and another for history. Each book is independent and can be updated individually, but they all live under one roof and share the same cataloging system (build tools, dependencies). You can easily see how a change in one book might reference another.

In short, a monorepo is about how you store and organize your code, while a monolith is about how you architect and deploy your application.

Advantages of a Monorepo

Storing all your code in one place has several key benefits:

• Simplified Dependency Management: You can have a single, shared set of dependencies for all projects, which helps avoid version conflicts.
• Improved Code Sharing and Collaboration: With all the code in one place, it's easier for teams to share and reuse code, leading to less duplication and more consistency.
• Atomic Commits: Changes that affect multiple projects can be made in a single commit. This makes large-scale refactoring much easier and ensures that the entire system is always in a consistent state.
• Centralized Tooling: You can use a single set of tools for building, testing, and deploying all projects, which simplifies the development workflow.

Disadvantages of a Monorepo

Of course, there are also challenges associated with this approach:

• Performance Issues: As the repository grows, it can become very large, leading to longer clone times and slower performance for Git operations.
• Tooling Complexity: Managing a large monorepo often requires specialized tools to handle the scale and complexity.
• Access Control: It can be more difficult to restrict access to specific parts of the codebase, as all code is in one repository.

Tools for Managing Monorepos

To tackle the challenges posed by monorepos, becoming familiar with some of Git's advanced features will be beneficial.

Here are a couple of native Git features that will be useful:

• Git LFS (Large File Storage): Monorepos can quickly accumulate large binary files. Git LFS helps manage these large files by keeping them out of the main Git history, which keeps the repository size manageable.
• Sparse Checkout: You don't always need to have every single file from a massive repository on your local machine. Sparse checkout allows you to check out only the specific folders or projects you need to work on, which can dramatically reduce the size of your working directory and improve performance.

How Do Submodules Compare?

When talking about monorepos, it's worth mentioning Git submodules as they offer another way to manage complex projects. A submodule is a Git repository embedded inside another Git repository.

Here's the key difference:

• Monorepo: A single, large repository containing all your projects. The integration is seamless, and all code shares the same history and release cycle.
• Submodules: You have a parent repository that points to specific commits in other, separate repositories. This keeps the project histories separate, which can be useful for third-party dependencies, but it can also make development more complex.

While submodules can be useful, they often introduce a more complicated workflow than a well-managed monorepo.

Is a Monorepo Right for You?

The decision to use a monorepo depends on the specific needs of your team and projects. For small, independent projects, a polyrepo approach might be simpler. But for large, interconnected systems where code sharing and consistency are important, a monorepo can be a very effective strategy.

By understanding the trade-offs and using the right tools, you can successfully manage a monorepo and reap the benefits of this powerful development approach.