Mastering Git Monorepos: A Beginner's Step-by-Step Guide

A monorepo is a Git repository that contains multiple projects, components, or libraries. It can be a good solution for managing large codebases with multiple dependencies, as it allows for easier code sharing and versioning across projects.

So let's follow the steps below:

Step 1

Create a new Git repository: Start by creating a new Git repository. For example, you could create a new repository called my-monorepo using the command line:

Step 2

Define your monorepo structure: Decide on the structure of your monorepo. For this example, let's say we want to create a monorepo for a web application that consists of multiple projects, including a frontend app, a backend API, and a shared library. Create a directory structure that reflects this:

Step 3

Add your projects: Add your existing projects to the monorepo. For each project, create a subdirectory in the monorepo and copy the project files into it. For example, to add the frontend app, we could do:

Repeat this process for the backend API and shared library projects.

Step 4

Set up Git submodules: Use Git submodules to manage dependencies between your projects. For example, let's say the frontend app depends on the shared library. To add the shared library as a submodule of the frontend app, navigate to the frontend directory and run:

This will add the shared library as a submodule in the shared-library subdirectory of the frontend directory.

Step 5

Create a build system: To build and test your projects, you'll need a build system that can handle dependencies between projects. For this example, let's use Bazel as the build system. Create a WORKSPACE file in the root directory of your monorepo, and add the Bazel rules for each project:

This defines the dependencies for each project and specifies the rules for building and testing them using Bazel.

Step 6

Add a root BUILD.bazel file: In the root directory of your monorepo, create a BUILD.bazel file that defines targets for building and testing the entire monorepo. For example, to build all projects and run their tests, you could define a target like this:

This defines a frontend_tests target that runs all test files in the frontend project, and a backend_image target that builds a Docker image for the backend API

Step 7

Commit changes: Commit your changes to Git:

Step 8

Manage your monorepo: You can now manage your monorepo using standard Git commands. For example, to update the shared library to a new version, navigate to the shared-library directory and run:

To update the frontend app to use the new version of the shared library, navigate to the frontend directory and run:

Step 9

Build and test your monorepo: To build and test your monorepo using Bazel, navigate to the root directory and run:

This will build and run all tests for all projects in the monorepo.

That's a brief overview of how to set up a Git monorepo using Bazel. Of course, the specifics will depend on your specific use case, but hopefully this gives you a good starting point.

Conclusion

In conclusion, using a Git monorepo can provide a number of benefits for managing multiple related projects or services. By keeping all the code in one repository, it becomes easier to share code between projects, enforce consistent coding practices and tooling, and manage dependencies. Using a build system like Bazel can also make it easier to build and test multiple projects in a monorepo.

However, setting up and managing a Git monorepo can be complex and requires careful planning and coordination. It's important to carefully consider the structure of your monorepo, including how to organize projects and dependencies, and to use tools like submodules and a build system to help manage complexity.

Overall, a Git monorepo can be a powerful tool for managing complex software projects, but it requires careful planning and management to be successful.