Monorepo vs. Multirepo: Managing Codebases in Modular Architectures

As we’ve covered monolithic vs. microservice architectures and introduced the concept of microfrontends, you’re now familiar with how modular applications can make development more scalable and flexible. However, as your project scales and you adopt these architectural patterns, you’ll face another critical decision—how to manage your codebase. This post will explore Monorepo and Multirepo approaches, helping you choose the best strategy for your project.

What Is a Monorepo?
A monorepo (short for "monolithic repository") is a single repository that contains all the code for multiple applications or services, including frontend, backend, and even shared libraries. With this approach, everything lives in one place, but it’s broken down into smaller packages or modules within the same repo.
Characteristics of a Monorepo:

• A single repository contains all code for multiple projects.
• Different applications or services share common libraries.
• One version control system (e.g., Git) manages the entire codebase.

What Is a Multirepo?
In contrast, a multirepo (or multi-repository) setup means that each service, application, or module is contained in its own independent repository. In a microservices environment, this could mean each microservice lives in a separate Git repository, with its own lifecycle and versioning.
Characteristics of a Multirepo:

• Each service or application has its own independent repository.
• Teams can develop and version-control their components separately.
• Code sharing between services requires careful management (e.g., via package registries).

Monorepo vs. Multirepo: Pros and Cons
Now that you understand the basic concepts, let’s dive into the pros and cons of each approach:

Pros of a Monorepo:

• Simplified Code Sharing Monorepos make it easy to share code between services, libraries, or components. If multiple services use a shared utility library, you can easily maintain and update it without complicated dependencies.
• Consistent Tooling Since all your projects are in the same repository, you can enforce consistent tooling (e.g., linting, testing, formatting) across the entire codebase.
• Atomic Changes A single commit can make changes across multiple services or components. This ensures consistency and makes refactoring easier.
• Improved Collaboration Developers can easily contribute across the entire codebase. You don’t need to worry about accessing or managing multiple repositories, which can streamline workflows.

Cons of a Monorepo:

• Scalability Issues As the project grows, managing a large monorepo can become challenging. Builds can take longer, and version control operations (e.g., cloning, branching) may slow down significantly.
• Risk of Code Bloat With everything in one place, the repo can become bloated with code, including features and services that may not be relevant to all team members.
• Access Control Managing permissions within a monorepo can be tricky, especially in larger organizations. Everyone who accesses the repo has access to everything unless fine-grained access controls are in place.

Pros of a Multirepo:

• Independent Lifecycles Each service or application in a multirepo has its own repository, versioning, and release cycle. This allows teams to work independently and reduces the risk of unintended changes affecting other services.
• Smaller, Focused Repositories Each repo is smaller and focused on a single service or application. This makes it easier to manage, especially as your project grows.
• Granular Access Control You can manage access on a per-repo basis, giving teams access only to the code they need. This is particularly useful in large organizations with many developers.

Cons of a Multirepo:

• Difficult Code Sharing Sharing code between services in a multirepo setup can be challenging. You need to manage dependencies manually and ensure that changes to shared libraries are synchronized across multiple repositories.
• Complex Tooling Each repository may require its own setup, including linting, testing, and build pipelines. This can introduce inconsistencies and make it harder to maintain a unified codebase.
• Cross-Repo Changes Making atomic changes across multiple repositories is much harder in a multirepo setup. You need to coordinate updates and ensure that changes are applied consistently across all relevant services.

Which One Should You Choose?
The decision between monorepo and multirepo depends on the size of your project, your team's structure, and your deployment needs. Here are some guiding factors:

When to Choose Monorepo:

• Small to Medium-Sized Teams: If your team is small and the project isn’t too large, a monorepo can simplify collaboration and reduce the overhead of managing multiple repositories.
• Tight Integration: If your services or components are tightly coupled and need to share a lot of code, a monorepo ensures that changes are propagated consistently.
• Unified Development Process: When you need a unified development environment with consistent tooling and atomic changes, a monorepo is the way to go.

When to Choose Multirepo:

• Large Organizations: For larger teams and organizations, a multirepo approach allows for independent development cycles and easier access control management.
• Microservices and Modular Frontends: If your application is built using microservices or microfrontends, and each component can operate independently, a multirepo setup allows for more flexibility.
• Separate Lifecycles: If different parts of your application are evolving at different paces, a multirepo setup lets teams manage their code without affecting others.

Hybrid Approach:
You don’t have to be strictly monorepo or multirepo. Many organizations adopt a hybrid approach, where a core set of related services or libraries are managed in a monorepo, while other services with less coupling are developed in separate repositories.

For example:

• Monorepo for Core Libraries: Shared utilities and libraries can live in a monorepo for easy access.
• Multirepo for Microservices: Each microservice can have its own repository, but they all rely on the shared core libraries from the monorepo.

This hybrid model provides the best of both worlds—ease of code sharing, along with independent development cycles.

Conclusion
Choosing between monorepo and multirepo isn’t a one-size-fits-all decision. Each approach has its strengths and weaknesses, and the right choice depends on your project’s complexity, your team’s size, and the level of autonomy you need. For smaller teams and projects that require tight integration, a monorepo might be the right choice. For larger, decentralized teams working on independent services, a multirepo setup offers greater flexibility.

What’s Next?
In the next post, we’ll look into API Versioning—when and how to version your APIs to ensure backward compatibility while continuing to evolve your application.