Repository Architecture: Exploring Monorepo, Multi-repo, and Beyond

Every development team, from a single freelancer to a multinational corporation, faces a fundamental question when starting a project: where are we going to put our code?

This decision, which may seem trivial at first, has profound implications for how we collaborate, manage dependencies, deploy our software, and, ultimately, for our productivity.

Today, we're going to break down the two most common strategies for organizing code: Monorepo and Multi-repo. We will objectively analyze their pros and cons to give you the information you need to decide. Additionally, we'll take a look at other approaches that exist across the spectrum.

Let's dive in!

The Traditional Approach: Multi-repo (or Poly-repo)

This is the strategy most of us are familiar with and the one that platforms like GitHub or GitLab naturally encourage. The idea is simple: every project, microservice, or library lives in its own independent repository.

Think of it as a chain of specialized bookstores: one for science fiction, another for history, another for crafts. Each one is autonomous, manages its own inventory, and has its own staff.

Advantages of Multi-repo

• Autonomy and Ownership: Each team owns its corner of the universe. They can choose their own tools, manage their deployment cycles, and move at their own pace. This fosters agility in independent teams.
• Tooling Simplicity: You don't need anything more than Git. Commands like clone, pull, or push are fast because the repositories are small and focused.
• Granular Access Control: Permission management is straightforward. Need someone to work on the payment service? You give them access to that repository and no other.
• Isolation and Decoupling: The physical barrier between repositories "forces" you to think in terms of well-defined APIs and to keep services decoupled, which is an excellent architectural practice.

Disadvantages of Multi-repo

• Dependency Hell: This is its biggest pain point. Imagine you have a shared library. If you make a change, you have to publish a new version and then go, one by one, to all 15 repositories that use it to update it. It's a slow, manual, and error-prone process.
• Complex Refactoring: Making a change that affects multiple services at once (e.g., modifying an endpoint and all its consumers) is a coordination nightmare. It requires multiple Pull Requests across different repositories and a perfectly orchestrated deployment.
• Code and Configuration Duplication: It's very easy to end up copying and pasting CI/CD configurations, linters, and other boilerplate files across dozens of repositories. Keeping them in sync is extra work.
• Knowledge Silos: Developers tend not to look beyond the repositories they work on. This makes it difficult to discover useful code that has already been written by other teams and can stifle innovation.

The Unified Approach: Monorepo

A monorepo inverts the previous logic: all of the organization's code, from every project and library, lives in a single, large repository.

Following the previous analogy, a monorepo is like a giant central library. It has sections for everything (API, frontend, mobile apps, shared libraries), but everything is under the same roof, managed by the same system. Companies like Google, Meta, and Microsoft are famous for using this approach at a massive scale.

Advantages of a Monorepo

• Total Visibility and Collaboration: Everyone can see all the code. This facilitates the discovery of existing code, encourages reuse, and allows for a better understanding of how different parts of the system interact.
• Atomic Refactoring: Its biggest strength. You can change an API and update all its consumers on the frontend and the mobile app in a single commit. The change is atomic: either everything works, or nothing gets merged. Consistency is guaranteed.
• Simplified Dependency Management: Say goodbye to versioning battles. All projects use the same version of external dependencies. Updating a library like React is done once for the entire ecosystem.
• Tooling Standardization: It's easy to enforce a single standard for code formatting, quality, and tools (tooling) across the entire organization, which increases consistency.

Disadvantages of a Monorepo

• Performance and Specialized Tooling: A repository with millions of files and years of history can make Git commands extremely slow. It becomes almost mandatory to use monorepo management tools like Nx, Turborepo, or Bazel, which have their own learning curves.
• CI/CD Complexity: Continuous Integration pipelines are more complex. They need to be smart enough to build and test only the projects affected by a change, rather than the entire repository.
• Risk of Coupling: The ease of importing code from anywhere can lead to developers creating unwanted dependencies if there isn't a clear architecture and discipline from the teams.
• Learning Curve: A new developer can feel overwhelmed by the size of the codebase and the need to learn the specific tools of the monorepo.

Quick Comparison Table

Beyond the Extremes: Other Approaches

Not everything is black and white. Hybrid approaches exist that try to get the best of both worlds:

• The Hybrid Approach: Some organizations keep their main services in separate repositories (multi-repo) but group key shared libraries and components in a monorepo.
• Meta Repositories (git submodules, etc.): Tools like Git submodules attempt to create a "repository of repositories." They allow you to nest one repository inside another. However, managing them is notoriously complex and they often introduce more problems than they solve. They are an option to consider, but one that must be studied carefully.

So, Which One Should You Choose?

As you've seen, there is no universal right answer. The choice is a strategic decision that depends on your circumstances. To decide, ask yourself these questions:

1. How related are my projects? If your projects share a lot of code and logic (e.g., a website, an API, and a mobile app that are all part of the same product), a monorepo can provide huge consistency benefits. If they are completely independent projects (e.g., websites for different clients), the multi-repo approach is more logical.
2. What is the size and structure of my team? Small, autonomous teams can thrive with multi-repos. Large organizations that need to maintain consistency across the board can benefit from a monorepo.
3. What level of pain am I willing to take on? Do you prefer the pain of coordinating multiple repositories (multi-repo) or the pain of learning and maintaining more complex tools (monorepo)?
4. What is my priority: autonomy or standardization? Your answer to this cultural question will give you a very clear hint.

Your Turn

Repository architecture is a lively and fascinating debate in the development world. Each approach has its champions and its detractors, and the best solution is always the one that works for you and your project.

And now, it's your turn:

• What approach do you use in your day-to-day work? Are you on #TeamMonorepo or #TeamMultirepo?
• What problems have you encountered and how have you solved them?

Let me know your thoughts in the comments! I would love to hear about your experience. You can also follow the conversation on my social media channels on X/Twitter and LinkedIn.

And if your company is grappling with this dilemma and you need a professional and experienced opinion to design your code and deployment strategy, don't hesitate to contact me at info@thedavestack.com. I'd be happy to help!