Mono-Repo vs Multi-Repo: A Deep Dive into Code Repository Strategies

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Hey there!

So you‘re trying to figure out whether to use a mono-repo or multi-repo for your next big project? I‘ve been there myself. As a longtime software engineer and open source contributor, I‘ve seen both approaches used successfully on large projects. In this guide, I‘ll share my insights to help you make an informed decision.

Mono repo vs multi repo

First off, what do these terms mean?

Mono-repo is when you store all your project‘s code and services together in a single repository.

Multi-repo splits things up into multiple repositories, with each one containing a separate component.

Now let‘s dive deeper into the pros and cons of each approach.

When Mono-Repo Works Best

Mono-repos shine for large projects with hundreds of developers collaborating closely together.

For example, Google uses a massive mono-repo with over 2 billion lines of code! The benefits for them include:

  • Easy to share and reuse common libraries across services
  • Avoid dependency versioning hell
  • Makes large-scale code refactoring smoother
  • Provides whole-system view for developers

Mono-repos also simplify code discoverability. There‘s only one place to look for any file or module you need. You can even implement custom search tools optimized for your codebase.

However, mono-repos introduce complexity when scaling to extremely large sizes. Facebook mitigated this by developing specialized infrastructure like a custom source control system. Most teams attempting mono-repo end up dealing with slower build times and unwieldy repositories.

When Multi-Repo Works Best

Multi-repo shines when you have clearly separated components and microservices. Top advantages:

  • Each service can evolve independently without affecting others
  • Repositories remain fast and lightweight
  • Services can be deployed on their own release cycle
  • Easy to enforce access control between teams
  • Enables continuous integration per service

Take Netflix as an example. They famously adopted a microservices architecture, which lends itself perfectly to multi-repo. Even a giant like Amazon uses this approach.

Multi-repo also prevents a monolithic codebase that bogs down developers. And it forces a modular architecture. The downside is you lose a unified code view, making it harder to grasp inter-service dependencies.

Key Differences Summarized

Here is a comparison of the two approaches:

Mono-Repo Multi-Repo
Single source of truth Own repo per component
Tightly coupled system Loosely coupled components
Heavy and complex Lightweight and modular
Shared libraries Duplicate common code
Global refactors Isolated changes
Unified development Siloed teams

Expert Opinions on the Debate

This topic has been heavily debated among software architecture experts. Here are some interesting perspectives:

Martin Fowler argues mono-repos may be the "pragmatic choice" for large projects due to benefits like single workflow and tribal knowledge sharing.

Uncle Bob claims decoupling components using multi-repo makes for "better architecture" following principles like SOLID.

Google engineers state mono-repo was crucial in enabling code reuse and global code ownership there.

So there are good points on both sides! The best choice depends on your specific constraints.

Making the Right Choice

When deciding between mono vs multi-repo, consider these factors:

  • Team structure and size
  • Amount of shared code
  • Rate of change to components
  • Deployment needs
  • Access control requirements
  • Developer productivity

For a large team building a highly integrated product, mono-repo may work best. For microservices with independent release cycles, multi-repo is likely the better fit.

You might even leverage a hybrid approach, maintaining some core libraries in a mono-repo and microservices in separate repositories. There are also tools like meta which essentially allow managing a mono-repo composed of multi-repos.

Key Takeaways

  • Mono-repo centralizes code for easier sharing while multi-repo partitions it into independent units
  • Mono-repo benefits collaboration but poses scaling challenges
  • Multi-repo enables decentralized ownership and modular architecture
  • Carefully examine your team, code and deployment needs when deciding
  • Hybrid approaches combining both models are also viable

I hope this guide gives you a balanced perspective on the mono-repo vs multi-repo debate! Let me know if you have any other questions.


Written by Alexis Kestler

A female web designer and programmer - Now is a 36-year IT professional with over 15 years of experience living in NorCal. I enjoy keeping my feet wet in the world of technology through reading, working, and researching topics that pique my interest.