Monorepos vs Polyrepos: Choosing the Right Structure for Your Project

As a computer science student and developer, I have worked on several projects that required structuring code across multiple services, libraries, or applications. One of the most common architectural decisions I have faced is whether to use a monorepo or a polyrepo. This choice impacts how teams collaborate, how code is shared, and how deployments are managed. In this post, I will compare both approaches, discuss the tools that support them, and provide practical guidance on when to choose each.

What is a Monorepo?

A monorepo is a single repository that contains multiple projects, libraries, or services. Instead of maintaining separate repositories for each component, everything lives in one place. This approach has gained popularity in recent years, largely due to tools that make managing large codebases easier.

Pros of Monorepos

Shared code and consistency When all code lives in one repository, sharing utilities, types, or components between projects is straightforward. You can import a local package directly without publishing it to a registry. This reduces duplication and ensures consistency across projects.

// Import a local package in a monorepo
import { formatDate } from '@my-project/utils';

Atomic commits and coordinated changes Making changes across multiple projects is easier because you can commit all related changes in a single commit. This is particularly useful when a change in a shared library affects multiple applications.

Simplified dependency management With a single lock file and a unified build process, managing dependencies becomes more predictable. Tools like Yarn Workspaces or npm Workspaces help resolve dependencies across packages without conflicts.

Cons of Monorepos

Repository size and performance As the codebase grows, the repository can become large and slow. Cloning, building, and running tests can take more time, especially if proper tooling is not in place.

Complex tooling requirements Managing a monorepo effectively requires tools that understand the structure of the codebase. Without proper configuration, builds and tests can become slow or unreliable.

Tight coupling risks If boundaries between packages are not well defined, projects can become tightly coupled. This makes it harder to evolve individual components independently.

What is a Polyrepo?

A polyrepo, or multi-repo, approach involves maintaining separate repositories for each project, service, or library. This is the traditional approach and is still widely used, especially in organizations with many independent teams.

Pros of Polyrepos

Clear boundaries and independence Each repository represents a distinct unit of work. Teams can work on their own repositories without worrying about impacting others. This is particularly useful in large organizations with many independent teams.

Smaller repositories Since each repository contains only the code for a specific project, cloning and building are faster. This is beneficial when working on a single service or application.

Simpler access control Access control is easier to manage because permissions can be set per repository. This is useful when different teams or external contributors need access to specific parts of the codebase.

Cons of Polyrepos

Code duplication and inconsistency Sharing code between repositories is more complex. You often need to publish packages to a registry, which adds overhead. This can lead to duplication or version mismatches.

Coordinated changes are harder Making changes that affect multiple repositories requires coordinating across multiple pull requests. This can slow down development and increase the risk of integration issues.

Dependency management overhead Each repository has its own lock file and dependency management. This can lead to inconsistencies, especially when shared dependencies are updated at different times.

Tools for Monorepos

Several tools have emerged to make managing monorepos easier. Here are three of the most popular ones:

Nx

Nx is a build system and project generator that provides powerful features for monorepos. It understands the dependencies between projects and can run tasks in parallel, cache results, and provide a visual graph of the project structure.

# Run a build for a specific project and its dependencies
nx build my-app

Nx is particularly useful for large monorepos with many interconnected projects. It also provides schematics for generating code and enforcing conventions.

Turborepo

Turborepo is a high-performance build system designed for JavaScript and TypeScript monorepos. It focuses on speed by caching task results and running tasks in parallel. It is lightweight and easy to set up.

// turbo.json
{
  "tasks": {
    "build": {
      "dependsOn": ["^build"],
      "outputs": ["dist/**"]
    }
  }
}

Turborepo is a good choice if you want a fast, minimal setup without the additional features of Nx.

Lerna

Lerna is one of the earliest tools for managing monorepos. It provides commands for bootstrapping, building, and publishing packages. While it has been largely superseded by newer tools, it is still used in some projects.

# Publish all changed packages
lerna publish

Lerna is a good choice for legacy projects or if you are already familiar with it. However, for new projects, I would recommend Nx or Turborepo.

When to Choose a Monorepo

A monorepo is a good choice when:

You have multiple projects that share code or dependencies.
You want to make coordinated changes across projects easily.
You have a small to medium-sized team that can manage a single repository.
You are using tools like Nx or Turborepo to manage the codebase.

For example, if you are building a web application with a frontend, backend, and shared utilities, a monorepo makes it easy to share types and utilities between the frontend and backend.

When to Choose a Polyrepo

A polyrepo is a good choice when:

You have many independent projects or services.
You have a large organization with many teams working on different parts of the codebase.
You need fine-grained access control for different parts of the codebase.
You want to keep repositories small and focused.

For example, if you are working on a platform with many independent microservices, each maintained by a different team, a polyrepo makes sense. Each team can work on their own service without worrying about the others.

Practical Takeaways

Start with a monorepo if you are building a small to medium-sized project with shared code.
Use tools like Nx or Turborepo to manage your monorepo effectively.
Choose a polyrepo if you have many independent projects or a large organization with many teams.
Do not be afraid to migrate from a polyrepo to a monorepo or vice versa as your project evolves.
Focus on clear boundaries and good tooling regardless of the approach you choose.