Choose Monorepo or Polyrepo for Your Project: An In-Depth Analysis

1. Understanding Monorepo and Polyrepo

Before we dig into the specifics, it’s essential to define what we mean by monorepo and polyrepo. Each has unique benefits and challenges, affecting how projects are structured, dependencies are managed, and code changes are deployed.

1.1 What is a Monorepo?

A monorepo (short for "monolithic repository") is a single repository that contains multiple projects, often spanning different services, libraries, and applications. Large companies like Google, Facebook, and Microsoft use monorepos to manage vast codebases, keeping their code in a centralized location to enhance consistency and collaboration.

Code Example: Suppose we have a monorepo structure that hosts both frontend and backend code for a web application. In this scenario, you may find a file structure as follows:

project-root/
├── frontend/
│   ├── package.json
│   └── src/
├── backend/
│   ├── pom.xml
│   └── src/
└── shared/
    ├── utils/
    └── constants.js

With this structure, the frontend and backend codebases are interconnected and share common utilities stored in the shared folder. Changes to shared resources, like utility functions or constants, instantly impact both the frontend and backend projects, which can be both an advantage and a challenge.

1.2 What is a Polyrepo?

A polyrepo structure, in contrast, comprises multiple repositories—typically one for each project, service, or library. Each repository is independent, allowing teams to manage each project separately. This model is widely adopted in microservices architectures, where each service operates in isolation.

Code Example: In a polyrepo approach, each component would be in its repository. For instance:

- frontend-repo/
    ├── package.json
    └── src/

- backend-repo/
    ├── pom.xml
    └── src/

- shared-utils-repo/
    └── src/

In this structure, the frontend and backend projects do not directly share a common folder. Instead, shared utilities may be referenced as dependencies, such as NPM or Maven packages, which keeps projects isolated but also introduces additional dependency management overhead.

2. Monorepo vs Polyrepo: Key Differences and When to Use Each

Both structures come with unique strengths and drawbacks, often depending on project size, team organization, and deployment needs.

2.1 Code Management and Dependency Sharing

In a monorepo, shared dependencies are easily managed as all projects exist within the same repository, simplifying dependency linking. This setup can reduce version conflicts and ensures that each service can use the latest shared code seamlessly.

However, in polyrepo, dependency sharing requires extra steps, such as publishing shared code as packages or modules. Although this can create more isolated environments, it also means updates to shared utilities require version bumps and dependency updates across repositories.

2.2 Build and Deployment Pipelines

Monorepos can complicate build and deployment pipelines, especially as the codebase scales. Tools like Bazel or Nx can optimize the process by only rebuilding affected parts of the codebase, but monorepos still require sophisticated infrastructure to maintain efficient builds.

Polyrepos often have simpler, more modular build and deployment pipelines. Each repository can maintain its independent pipeline, allowing teams to deploy services independently. However, managing numerous pipelines can be challenging, particularly in large-scale projects.

2.3 Code Ownership and Collaboration

With monorepos, teams working on different parts of the project can more easily collaborate. Shared ownership also encourages a more unified code style and adherence to best practices across the codebase.

In a polyrepo model, code ownership tends to be more distinct, which may better suit organizations with multiple independent teams. This structure can help reduce merge conflicts and align with the autonomy often desired in microservices.

2.4 Version Control and Change Management

Monorepos can make change management straightforward. Teams can make atomic commits that affect multiple services, allowing for easy tracking of cross-service changes. However, this structure can also lead to larger commit histories, potentially slowing down version control operations over time.

In a polyrepo setup, each repository maintains its own history, making the codebase easier to navigate. Yet, managing multiple repositories often leads to greater overhead in synchronizing changes across services, especially when multiple services rely on shared functionality.

3. Best Practices for Monorepo and Polyrepo Structures

Deciding which structure to adopt should involve analyzing your team’s needs, project size, and long-term scalability requirements. Here are some best practices to keep in mind.

3.1 Monorepo Best Practices

• Use a Robust Build Tool: Monorepos often require complex builds, so consider using tools like Bazel, Lerna, or Nx that are designed to handle multi-project repositories.
• Implement Access Controls: In large organizations, access control is vital. Use branch and permission settings to prevent unauthorized changes across projects.
• Regularly Clean Up Unused Code: Monorepos can accumulate unused code over time. Periodic reviews help maintain efficiency.

3.2 Polyrepo Best Practices

• Automate Dependency Management: Tools like Dependabot and Renovate can help automate version updates, reducing the overhead of managing shared code.
• Standardize CI/CD Pipelines: Standardized deployment scripts and environments streamline management across repositories, even as projects grow.
• Establish Clear Ownership: Defining ownership of each repository clarifies responsibilities, reduces conflicts, and fosters accountability within teams.

4. Key Factors to Consider When Choosing Between Monorepo and Polyrepo

The choice between monorepo and polyrepo is highly situational. Here are key factors to evaluate.

Team Size and Structure

Larger teams with distinct roles may benefit from polyrepos to promote isolated, independent workflows. Smaller teams working on interconnected projects may find monorepos more efficient, as they simplify collaboration and dependency management.

Complexity of Inter-Dependencies

Projects with heavy dependency sharing or where services are tightly coupled often function better in a monorepo, reducing dependency conflicts and synchronization issues. On the other hand, if projects are largely independent, polyrepo allows for cleaner separation.

Tooling and Infrastructure Support

Monorepos require tools that can handle the scale, such as Bazel for builds or Nx for organizing projects. Polyrepos may be better suited to projects using simpler tooling setups or requiring independent deployment pipelines.

5. Conclusion

Selecting the right repository structure is a decision that can shape your development workflow and codebase management practices. Monorepos centralize resources and facilitate tight integration, whereas polyrepos offer flexibility and independence, especially suited for distributed teams and loosely-coupled services. Ultimately, the choice depends on your team’s specific needs, project complexity, and long-term goals.

Are there questions or specific scenarios you’re curious about? Drop your comments below, and let’s discuss how these strategies apply to your projects.