The Monorepo Mania: A Critical Look

In the world of software development, the debate between monorepos and multi-repos has been a longstanding one. While monorepos have gained significant popularity, especially among tech giants like Microsoft, Facebook, and Twitter, the idea that they are always the best solution is a fallacy. Let’s dive into the nuances of both approaches and explore why, in many cases, multiple repositories might be the better choice.

Understanding Monorepos and Multi-Repos

Before we get into the nitty-gritty, let’s define what we’re talking about:

Monorepo

A monorepo is a single repository that contains all the necessary code for various projects. This approach is often associated with microservices architecture and can foster better collaboration, visibility, and speed in development. Here’s a simple diagram to illustrate this:

graph TD A("Monorepo") -->|Contains|B(Project 1) B("Monorepo") -->|Contains|C(Project 2) C("Monorepo") -->|Contains|D(Project 3) B -->|Depends on| C C -->|Depends on| D

Multi-Repo

A multi-repo approach involves housing each project or component in a separate repository. This method offers autonomy for different teams, better isolation, and more flexible workflows.

graph TD A("Repo 1") -->|Project 1|B(Repo 2) -->|Project 2|C(Repo 3) -->|Project 3| A -.->|Independent| B B -.->|Independent| C

The Allure of Monorepos

Monorepos have several compelling advantages that make them attractive to many developers:

  • Visibility and Collaboration: With all code in one place, it’s easier for developers to see what’s going on across different projects. This visibility enhances security and fosters a collaborative environment where developers can share and reuse assets efficiently[1][3][5].
  • Speed and Atomic Changes: Monorepos allow for atomic changes across multiple projects with a single action, which can significantly accelerate development. This is particularly useful when making application-wide refactorings or ensuring that all tests run across all libraries[3][5].
  • Consistency and Code Reusability: Monorepos promote consistent coding practices and facilitate code reuse. When similar functionalities are required in multiple projects, developers can implement and maintain them in a single location, reducing duplication and ensuring uniformity[5].

The Pitfalls of Monorepos

Despite these advantages, monorepos are not without their drawbacks:

  • Scalability Issues: As the codebase grows, monorepos can become increasingly difficult to manage. Git performance can slow down, and the sheer size of the repository can make it cumbersome to work with[4].
  • Access Control and Security: Monorepos often require sophisticated permission management systems because everyone with access to the repository can see all the code. This can be a significant security risk if not managed properly[1][4].
  • Onboarding Complexity: New team members may face a steep learning curve when joining a project with a large monorepo. The initial setup can be complex, and the documentation may not always be complete[3].

When Multi-Repos Shine

While monorepos have their strengths, there are several scenarios where multi-repos are the better choice:

Independent Projects

If your projects are largely independent with minimal code sharing or dependencies, a multi-repo approach can provide more autonomy and flexibility for individual teams or projects. Here’s how it looks:

sequenceDiagram participant Team A as "Team A" participant Team B as "Team B" participant Repo A as "Repo A" participant Repo B as "Repo B" Team A->>Repo A: Work on Project A Team B->>Repo B: Work on Project B Note over Team A,Team B: Independent workflows

Security and Access Control

When projects have distinct security, access control, or confidentiality requirements, separate repositories can provide better isolation and control over who can access different parts of the code. Here’s an example:

graph TD A("Team A") -->|Access|B(Repo A) B("Team B") -->|Access|D(Repo B) B -.->|No Access| C D -.->|No Access| A

Diverse Workflows

Different projects may require diverse development workflows, programming languages, or tools. In such cases, separate repositories can accommodate these variations without affecting others.

graph TD A("Repo A") -->|Uses|B(Tool A) B("Repo B") -->|Uses|D(Tool B) B -.->|Different| D

Practical Considerations

Versioning and Releases

In a multi-repo setup, each repository can be versioned and released independently, which is particularly useful when different parts of the system change at different rates. Here’s a flowchart illustrating the process:

flowchart LR A[Tag_Repo_A] --> B[Release Project A] B[Tag_Repo_B] --> D[Release Project B] B -.->|Independent| D

Forking and Contributions

For open-source projects or contributions, multiple repositories make it easier for contributors to focus on specific projects without needing to navigate a large monorepo. Here’s how it works:

sequenceDiagram participant Contributor participant Repo A as "Repo A" participant Repo B as "Repo B" Contributor->>Repo A: Contribute to Project A Contributor->>Repo B: Contribute to Project B Note over Contributor,Repo A,Repo B: Easy navigation

Conclusion

The choice between a monorepo and a multi-repo setup is not a one-size-fits-all decision. While monorepos offer significant benefits in terms of collaboration, visibility, and speed, they also come with scalability issues, access control challenges, and onboarding complexities.

Multi-repos, on the other hand, provide autonomy, better isolation, and flexibility, making them ideal for projects with independent workflows, diverse requirements, or stringent security needs.

Ultimately, the decision should be based on the specific needs and scale of your projects, the number of engineers involved, and the project timeline. By understanding the pros and cons of each approach, you can make an informed decision that best suits your team’s needs and enhances your development workflow.

So, the next time someone says, “Always use a monorepo,” you can smile knowingly and say, “Not so fast, my friend. Let’s consider the bigger picture.”