Monorepo vs Multi Repos: A Comprehensive Comparison

Recently I was working on motivating more teams, to start using monorepo technology with very clear reasons, and those reasons I want to share with you.

The first miss conception is,  Monorepo is the same as a monolith.
This completely depends on your usage of the monorepo.

A monolith could be managed in a monorepo. But a monolith could also be split into multiple repositories. Similarly, a monorepo could be used with microservices instead of a monolith.

So what are monorepo and multi-repo?

When it comes to version control and project management, there are two main approaches that developers can use: monorepos and multi-repos. Monorepos, short for monolithic repositories, refer to a version control strategy in which all projects within an organization are stored in a single repository. Multi-repos, on the other hand, involves using multiple repositories to store and manage projects. In this article, we'll compare the two approaches and examine the pros and cons of each.

One major advantage of monorepos is their ability to improve repository management. With a multi-repo approach, upgrading a software version or making other changes to individual repositories can be a time-consuming and error-prone process. For example, let's say that you have 10 repositories in your company, all managed in GitLab and using a specific version of Node.js in the GitLab-CI configurations. If you want to upgrade Node.js to the latest LTS version, you have two options:

• Point all of your repositories to the latest tag and update the latest version in one place. This might lead to unexpected issues, as some projects may not be ready for migration yet.
• Manually migrate each repository to support the latest version of Node.js. This is an O(n) process, meaning that the amount of work you have to do is directly related to the number of repositories you have.

With a monorepo approach, upgrading Node.js or making other changes is much simpler. You only have to update the version in a single CI configuration and test all of the projects in the monorepo to ensure that everything is working as expected. This can save time and reduce the risk of unexpected issues arising.

Another advantage of monorepos is their ability to better handle relationships between repositories. In a multi-repo setup, it can be difficult to keep track of how changes in one repository might affect others. For example, if you make a change to a library (Lib A) that is used by multiple other projects, you'll need to test each of those projects to ensure that the change didn't break anything. This can be a time-consuming process, especially if you have a large number of consumers of Lib A. With a monorepo approach, you can use tools like Turborepo and Nx to automatically trigger tests for affected areas, saving time and increasing overall stability.

Monorepos also make it easier to detect and prevent code duplication. With a multi-repo approach, detecting duplicate code across multiple repositories can be a labor-intensive process that requires domain expertise or specialized technological solutions. In a monorepo, on the other hand, tools like SonarCube can be used to analyze the entire repository and detect duplicate code. This can then be refactored into a library and shared across projects, reducing maintenance and improving code quality.

In addition to these technical benefits, monorepos can also improve collaboration and facilitate the growth of domain expertise within an organization. By allowing all projects to be managed in a single repository, monorepos make it easier for developers to see the big picture and understand how their work fits into the overall project. This can lead to better collaboration and faster problem-solving, as well as a more shared understanding of the codebase and the business domain.

While there are certain situations where a multi-repo approach may be more appropriate, the use of monorepos is becoming increasingly popular in the software development industry. That said, it's important to consider the pros and cons of each approach before deciding which is right for your project. Monorepos offers several benefits, but they may not be suitable for all projects, and they can become unwieldy as they grow in size.

So, when should you use a monorepo, and when should you use a multirepo? Here are some pros and cons to consider:

Pros of monorepos:

• Improved repository management: Monorepos allows developers to make changes to multiple projects at once, using advanced tools to detect and test affected areas. This can save time and increase overall stability.
• Better handling of relationships between repositories: Monorepos make it easier to see the relationships between projects and automatically trigger tests for affected areas, improving overall stability and saving time.
• Easier detection and prevention of code duplication: Monorepos make it easier to detect and prevent code duplication, using tools like SonarCube to analyze the entire repository and refactor duplicate code into shared libraries.
• Improved collaboration and domain expertise growth: Monorepos facilitate better collaboration and understanding of the codebase and business domain, leading to faster problem-solving and a shared understanding of the project.

Cons of monorepos:

• Initial setup may be more complex: Setting up a monorepo can be more complex than setting up multiple repositories, especially if the project is already well established.
• Harder to manage large monorepos: Monorepos can become unwieldy as they grow in size, making it harder to manage and navigate the codebase.
• May not be suitable for projects with a strong separation of concerns: If a project has a strong separation of concerns or very distinct sub-projects, a monorepo may not be the best choice. In these cases, a multi-repo approach may be more appropriate.

Pros of multi-repos:

• Simplicity: Setting up and managing multiple repositories can be simpler than managing a single monorepo, especially for small projects or projects with a strong separation of concerns.
• Better suited for large teams: In some cases, multi-repos may be better suited for large teams or projects with many distinct sub-projects, as they allow for more flexibility and separation of concerns.

Cons of multi-repos:

• Increased complexity: Managing multiple repositories can be more complex than managing a single monorepo, especially as the number of repositories grows.
• Harder to handle relationships between repositories: It can be difficult to keep track of how changes in one repository might affect others in a multi-repo setup, leading to a need for more extensive testing and the risk of unexpected issues arising.
• Increased risk of code duplication: Detecting and preventing code duplication is more difficult in a multi-repo setup, as it requires specialized tools or domain expertise.
• Reduced collaboration and domain expertise growth: With a multi-repo approach, it can be harder for developers to see the big picture and understand how their work fits into the overall project, leading to reduced collaboration and slower problem-solving.

Ultimately, the choice between a monorepo and a multi-repo approach will depend on your specific needs and the nature of your project. Both approaches have their pros and cons, and what works for one project may not work for another. Carefully consider the trade-offs and choose the approach that makes the most sense for your situation.