Monorepos: Are They a Good Thing?

In the world of software development, managing source code effectively is crucial for the success of projects, especially as they scale. One of the most important decisions teams must make is how to structure their codebase: using a monolithic repository (monorepo) or multiple repositories (multirepo).

This article explores the advantages and disadvantages of adopting a monorepo, with a focus on how platforms like GitHub and Azure DevOps support this model.

What is a Monorepo?
A monorepo is a version control strategy that involves storing all the code for multiple projects within a single repository. This approach is contrasted with a multirepo strategy, where each project or service has its own repository. Large tech companies such as Google and Facebook have popularized the use of monorepos, but its adoption varies based on organizational needs and preferences.

Let's start with a look at some reasons why you might want to use a monorepo strategy.

Pros of Using a Monorepo

1. Simplified Dependency Management
One of the most significant advantages of a monorepo is the simplification of dependency management. In a monorepo, shared libraries and services are kept within the same repository, making it easier to manage dependencies across multiple projects.

For instance, when a shared library is updated, all dependent projects within the monorepo can be immediately tested with the new version, ensuring compatibility and reducing the risk of integration issues. Platforms like GitHub support monorepos through robust branching and tagging features that help manage different versions of dependencies in a single repository.

2. Unified Versioning and Coordination
Monorepos allow teams to implement unified versioning for all projects within the repository. This ensures that every component of the system is compatible and up-to-date with the others, facilitating easier tracking of changes and regressions. With tools such as Azure DevOps, teams can leverage build and release pipelines that apply across all projects in the monorepo, enabling consistent deployment processes and reducing overhead in managing separate pipelines for each repository.

3. Streamlined Workflow and Tooling Consolidation
Adopting a monorepo can significantly streamline the development workflow and consolidate tooling across multiple projects. By having a single repository, teams can standardize on a single set of tools for version control, continuous integration (CI) and continuous deployment (CD). This uniformity eliminates the need for developers to switch contexts between different projects and tools, which can enhance productivity and reduce the learning curve for new team members.

For example, platforms like GitHub and Azure DevOps support comprehensive CI/CD pipelines that can be configured once and utilized across all projects within the monorepo. This not only simplifies the development process but also ensures consistency in build and release practices across the entire organization.

Of course, there are also reasons why a monorepo may not be right for you.

Cons of Using a Monorepo

1. Scalability Challenges
As the number of projects in a monorepo grows, so does the complexity and size of the repository. This can lead to scalability issues such as slower build times and more cumbersome repository management. Tools like GitHub and Azure DevOps offer features like sparse checkouts and selective builds to mitigate these issues, but they require additional configuration and maintenance, which can be a burden for large teams or projects.

2. Increased Complexity in Access Control
Managing access rights in a monorepo can be more challenging than in multirepos. Since all projects are contained within a single repository, ensuring that only authorized personnel have access to specific parts of the codebase can be complex. Although platforms like Azure DevOps provide granular access control mechanisms, setting up and maintaining these permissions can be intricate and error-prone.

3. Risk of Coupling and Tight Integration
The convenience of having all projects in one repository can inadvertently lead to tight coupling of unrelated projects. This coupling can make it difficult to isolate projects from one another, leading to potential issues when changes in one project adversely affect others. Such integration risks can complicate refactoring and scaling efforts, making it harder to manage the codebase as the number of projects increases.

Conclusion
Choosing between a monorepo and multirepo setup depends on the specific needs and context of the development team. While monorepos offer significant advantages in terms of simplified dependency management, unified versioning and ease of code reuse, they also come with challenges related to scalability, complexity in access control and risk of tight integration.

Tools like GitHub and Azure DevOps provide features that can help mitigate some of these challenges, but they also require careful configuration and management. Ultimately, the decision should be guided by the specific operational and strategic goals of the organization.

Posted by Mickey Gousset on 05/23/2024