Software teams require a dependable method for maintaining organization within their programming codebase during project development. One of the key architectural decisions teams face is choosing between different repository structures. Here, the debate of monorepo vs polyrepo becomes crucial.

Organizations face huge challenges when transitioning between monorepo vs polyrepo microservices once they have already started a project. The complex nature of development leads developers to struggle with both dependencies that are hard to manage and tightly bound code modules and intricate CI/CD pipelines that become challenging to separate. 

Converting from Monorepo and Polyrepo (or vice versa) will typically cause broken builds and dependency mismanagement and extended integration durations. 

Monorepo vs Polyrepo

A Monorepo designates a unique version-controlled repository that exponentially expands by incorporating more projects and service libraries. The organization houses all code within a single central repository, which provides teams with one location to share and work together on their code.

The Polyrepo repository model stores each project component service in distinct version-controlled repositories, which are known as multiple repositories. This separation of services into distinct repositories occurs in microservices and large organizations operating with independent teams.

Monorepo Code Structure

Uses a Single Build Tool for Everything

• Bazel and Nx, along with Lerna and Turborepo serve as typical tools that manage efficient build processes.
• All projects benefit from uniform build processing through this system.

Follows a Unified Directory Structure for Projects

Example Monorepo layout:

• Apps: Contains different services like frontend, backend, or microservices.
• Packages: Shared utilities, UI components, or business logic.
• Configs: Centralized configuration files (ESLint, Prettier, CI/CD settings).
• Scripts: Automation scripts for deployment and maintenance.

Polyrepo Code Structure

Each Service Operates Independently

• Each project, along with its services, exists in separate repositories which maintain individual independence.

Example Polyrepo structure with repositories:

• The services run autonomously with independent build processes, deployment protocols, and version management techniques. Since each service is built separately, builds are typically faster as they do not depend on other services or shared repositories.
• The separate repositories containing shared library components (such as UI elements and database interfaces) require manual import procedures.

Tools for Managing Monorepos

Efficient Monorepo management relies on specialized tools that optimize the efficiency of build processes and dependency control, together with CI/CD workflow automation. These performance optimization tools, complexity reduction techniques, and scalability tools operate effectively within large codebases.

Popular Monorepo Tools

1. Bazel – High-Performance Build System

The polyglot build and test functionality named Bazel stands as a tool developed by Google for handling large-scale Monorepo requirements. It provides.

• The build system runs incrementally by compiling only affected source files.
• Remote caching functions as a system to accelerate builds performed on various machines.
• Through its language support, Bazel accepts Java, Go, Python, C++, and much more.

Example Bazel build file (BUILD.bazel) for a Node.js project:

hello.js content: 

BUILD contents:

• The entry point of the project exists in src/index.js, while dependencies are located in //src/utils.
• The system will rebuild only files that experience modifications to achieve higher operational efficiency.

2. Lerna – JavaScript/TypeScript Monorepo Management

Lerna serves as a management solution for package versions and dependencies, along with publishing features through Yarn Workspaces in Monorepos.

Setting up Lerna with Yarn Workspaces (lerna.json):

• Manages multiple packages inside packages/*.
• Each package operates with its individual version numbers under independent versioning.

Running Lerna commands:

Output:

Tools for Managing Polyrepos

Polyrepos separate different services or projects into individual repositories. Polyrepo management needs version control strategies with CI/CD automation, dependency management, and a service discovery tool for effective efficiency.

Popular Polyrepo Tools

1. Git Submodules & Git Subtrees – Managing Shared Code

Git Submodules, together with Git Subtrees, establish dependency connections across different repositories without merging their contents.

Git Submodules permit developers to incorporate external repositories into their main repository without combining their historical versions.

The Git Subtrees system allows you to merge queues outside repositories with a maintained historical connection between them.

Adding a Git Submodule:

• The process adds shared-library to the submodule section within the libs/ directory.
• Updates and initializes submodules recursively.

Using Git Subtrees:

• The command extracts shared-library from an external repo and adds it to libs/ without creating individual change logs.

2. Jenkins + GitHub Actions

The CI/CD pipelines of Polyrepos need to handle build and deployment management across various repositories.

• Jenkins:
  The system provides automated pipeline functionality, which controls distributed repository builds through Jenkinsfiles.

• GitHub Actions:
  Helps automate CI/CD workflows within individual repositories while orchestrating cross-repo operations.

• Pros: Integrates well with Polyrepo structures, enabling independent builds and deployments.
• Cons: Requires manual coordination between repositories.

Best Practices for Using Monorepos

Monorepo provides code-sharing simplicity while maintaining dependency control yet developers must follow structural best practices to maintain scalability. Let’s explore guidelines for code organization, CI/CD optimization methods,  dependency management requirements, code review practices, and deployment approaches.

Organizing Code Effectively

As a repository grows, the proper structure of a Monorepo helps prevent technical debt while keeping everything clear.

1. Use Strict Linting Rules

• All teams must follow coding standards through the combined use of ESLint and Prettier as tools for enforcement.

• The formatting system ensures all code follows a standard design, which avoids merge conflicts during pull requests.

2. Implement a Modular Folder Structure

• Effective directory organization provides structural ordering to projects.

• The apps contain independent applications.
• The packages are shared libraries reusable utilities.
• The directory contains configuration files for testing ,linting and building.

Shifting from a monorepo vs polyrepo introduces new challenges, such as maintaining consistency across repos, and handling dependencies. 

Best Practices for Using Polyrepo

Polyrepo structures enable better service independence, self-governing teams, and scalability, but effective management of multiple repositories depends on strategic organization, reliable CI/CD, dependency control, and structured release techniques. This part introduces the recommended approaches to sustain and grow Polyrepo architectural systems.

Organizing Code Effectively

System-wide consistency among multiple repositories becomes necessary for efficient repository management.

Use Git Submodules or Subtrees for Shared Code

Git Submodules and Subtrees enable the management of common libraries, which multiple service repositories require.

Example: Adding a Git Submodule for a shared library

• Shared code can be used repeatedly in different repositories because of this approach.

Code Reviews & Access Control

Multiple repository management requires fundamental attention to both code quality standards and access control systems.

1. Use CODEOWNERS for Repository Ownership

• The tool distributes different teams to manage specific repositories.

2. Enforce Branch Protection Rules

GitHub and GitLab require branch protection rules that stop unauthorized merge activities.

• The system helps maintain both exceptional PR quality and stops improper merge activities from occurring.

Now let’s review two of the largest companies’ strategies to get an idea of what may be best for your needs.

Facebook and Netflix Repository Strategies

Facebook and Netflix manage millions of daily commits while operating massive distributed systems with highly refined CI/CD workflows. Their repository approaches have distinct characteristics because of their technical requirements.

Facebook: Monorepo with Mercurial & Buck

Repository Strategy

• Facebook maintains a Monorepo system for its essential applications even though it avoids this approach for other projects.
• The system uses Mercurial as its primary repository solution to achieve better scalability.
• The Facebook Monorepo contains all web mobile and backend code within its single repository.

Why Monorepo?

• The system permits teams to share library files along with code features throughout different teams.
• This approach enables modifications to affect various services as single units during atomic commits.
• The system eases the process of managing dependencies between backend and frontend developers.

Tools Used

1. Mercurial (Hg) scales better than Git for large repositories.
2. The Facebook team developed Buck as their proprietary high-performance build system.
3. Watchman performs file change monitoring to enhance build and testing efficiency.
4. Phabricator is used for code review and workflow management.
5. EdenFS delivers improved file system performance to enhance the development process of extensive codebases.

The Monorepo strategy of Facebook succeeds because the company developed proprietary tools which enhance Git performance capabilities.

Netflix: Polyrepo with Microservices & CI/CD Automation

Repository Strategy

• Netflix’s approach to monorepo vs polyrepo leans toward Polyrepo, distributing services across individual repositories for better scalability.
• Netflix’s management team operates individual repositories, each corresponding to a distinct service component, ranging from content recommendation engines, playback and encoding services to infrastructure management tools.
• Every service operates with exclusive independence for development deployment and scaling tasks.

Why does Netflix use a Polyrepo structure?

• High autonomy exists within this system, which permits teams to select various technologies.
• Enables independent deployments, reducing risk for large-scale releases.
• Scales well with hundreds of microservices running in production.

Tools Used

1. The version control systems GitHub and GitLab serve distributed repositories.
2. Netflix operates Spinnaker as its dedicated platform for CI/CD automation of deployments.
3. The deployment process the testing function, and builds fall under Jenkins and GitHub Actions management.
4. Terraform & Spinnaker function together as a system that allows users to control infrastructure through code.
5. Kubernetes & Helm operates as an orchestration system while managing service scaling operations.
6. GraphQL & gRPC mainly manages inter-service communication.

The Polyrepo approach at Netflix functions effectively because automated processes, strong DevOps methods, and CI/CD mechanisms allow the microservices architecture to run efficiently.

Choosing Between Monorepo and Polyrepo

When deciding between monorepo vs polyrepo pros and cons, your approach should align with team size, project complexity, and collaboration needs to ensure optimal development efficiency.

• Monorepo provides the best results when your team requires common dependencies as well as unified development pipelines and CI/CD management.
• The Polyrepo approach delivers superior results to teams that need independent scalability and isolation between services, along with flexible tool choices.

FAQs

Q1: Is Monorepo Better Than Polyrepo?

There is no one-size-fits-all answer. Monorepo works exceptionally well for teams that need shared libraries and unified build processes, yet Polyrepo stands out when teams need autonomous service development and independent service expansion capabilities. Your team should select the repository model that best supports its existing workflow with CI/CD requirements and development objectives.

Q2: Which Companies Use Monorepos?

Many large tech companies leverage Monorepos:

• Google operates an enormous Monorepo under Piper and Bazel management.
• Facebook uses Mercurial-based Monorepo for its codebase.
• Uber operates a Monorepo setup through the combination of Buck and Bazel.
• Microsoft uses a hybrid Monorepo approach for projects like TypeScript and Azure.

Q3: Can I Migrate From Polyrepo to Monorepo?

The migration can succeed through deliberate planning followed by proper execution.

• The first step requires identifying all shared libraries together with the service interaction patterns.
• Implement Nx Lerna Bazel as your upgrade tool.
• The existing CI/CD pipelines must be modified to function for one repository.
• The process of service migration should take place through stages while keeping each phase stable.
• The repository speed needs optimization through performance monitoring to prevent slow build times.