MonoRepo

A monorepo, short for monolithic repository, is a version control repository that holds multiple projects, often related or dependent on each other, under a single repository. In contrast, a polyrepo (multiple repositories) approach would involve each project having its own separate repository.

Reasons for Monorepos:

Code Sharing:

In a monorepo, projects can easily share code and dependencies. This can lead to improved code consistency and reduced duplication.

Atomic Changes:

It allows for atomic changes across multiple projects, ensuring that changes in one project do not break others.

Cross-Project Refactoring:

Developers can perform large-scale refactoring across the entire codebase more easily, ensuring consistent changes across projects.

Single Source of Truth:

There’s a single source of truth for configuration files, build scripts, and other development-related files, reducing the risk of inconsistencies.

Easier Dependency Management:

Managing dependencies becomes more straightforward as they are centralized and shared among projects.

Streamlined CI/CD:

Continuous Integration (CI) and Continuous Deployment (CD) pipelines can be set up more efficiently, as the entire codebase is in one place.

Simplified Versioning:

Versioning becomes simpler as all projects are versioned together, reducing compatibility issues.

Challenges Addressed:

Dependency Hell:

Monorepos can help alleviate dependency management issues by centralizing dependencies.

Consistency:

Ensures consistency in code style, conventions, and configurations across projects.

Cross-Project Collaboration:

Facilitates collaboration and communication between developers working on different projects.

Atomic Changes Across Projects:

Helps avoid scenarios where a change in one project breaks another, as changes can be made atomically across projects.

Structure of MonoRepo

The ideal structure for a monorepo depends on the specific needs and characteristics of your projects and development team. However, here is a generalized guide for structuring a monorepo:

1. Root Level:

• /packages: This directory holds all the individual packages or projects within the monorepo. Each package can represent a separate application, library, or module.
• /scripts: Place common scripts or tools that are used across multiple packages.
• /docs: Include documentation that spans multiple packages.
• /config: Store configuration files that are shared among packages.

2. Package Structure:

• /packages/app1: A specific package directory for each application, library, or module. Each package can have its own structure based on its nature.
• src/: Source code for the package.
• tests/: Unit tests and integration tests.
• public/: If it's a web application, this directory might contain static assets.
• dist/: Build artifacts and compiled code.
• package.json: Dependency management and package-specific configuration.

3. Shared Code:

• If there is shared code among packages, it can be organized in a few ways:
• Common Module:
• /packages/common: A package specifically for shared code that can be used by other packages.
• In-Place Sharing:
• Shared code can be kept in a shared directory within each package.

4. Configuration:

• /config: Store configuration files that are shared among packages.
• /scripts: Common scripts or tools that can be shared across packages.

5. Versioning:

• Use a tool like Lerna to manage versioning, releases, and linking of packages within the monorepo.

6. Build and CI/CD:

• Implement a centralized build system that can build and test the entire monorepo or specific packages.
• Configure CI/CD pipelines to handle the deployment of individual packages or the entire monorepo.

7. Documentation:

• Include a centralized documentation folder, such as /docs, where you can maintain documentation that spans multiple packages.

Example Structure:

/monorepo-root
  /packages
    /app1
      /src
      /tests
      /public
      /dist
      package.json
    /app2
      /src
      /tests
      /public
      /dist
      package.json
  /scripts
  /config
  /docs
  lerna.json

Decision Criteria:

Deciding whether your project needs a monorepo or not depends on several factors:

Codebase Size and Complexity:

Monorepos are particularly beneficial for large and complex codebases with interdependencies.

Team Structure:

If your development team works on multiple projects simultaneously and there’s significant code sharing, a monorepo might be beneficial.

Interdependencies:

If your projects have tight interdependencies and need to be versioned and released together, a monorepo can simplify this.

Build and CI/CD Efficiency:

Monorepos can make it easier to set up efficient build and CI/CD processes for multiple projects.

Developer Workflow:

Consider whether a monorepo aligns with the preferred workflow of your development team.

Tooling Support:

Ensure that the tools and version control system you use provide good support for monorepos.

Maintenance Overhead:

Consider the maintenance overhead of managing a monorepo, especially if your projects can function independently.

Challenges with Monorepo

1. Scaling Issues:

• Challenge: As the codebase grows, handling a large number of files and projects within a single repository can lead to scalability issues.
• Resolution: Implement build optimizations, leverage incremental builds, and use tools that are designed to scale with large codebases. Additionally, consider breaking down the monorepo into smaller logical units if necessary.

2. Increased Repository Size:

• Challenge: A monorepo can become large in terms of storage, making it challenging to clone and manage.
• Resolution: Employ techniques such as shallow cloning and sparse checkouts to reduce the size of local working copies. Additionally, consider using Git LFS (Large File Storage) for managing large binary files.

3. Build and Test Times:

• Challenge: Running builds and tests across the entire monorepo can be time-consuming.
• Resolution: Implement selective building and testing to execute only the necessary parts affected by the changes. Explore distributed build systems and caching strategies to speed up build times.

4. Dependency Management:

• Challenge: Managing dependencies across multiple projects can be complex and error-prone.
• Resolution: Use dependency management tools specifically designed for monorepos, such as Yarn Workspaces or Lerna. Centralize dependency versions, and ensure consistency in dependency configurations.

5. Tooling and Ecosystem Support:

• Challenge: Some tools and third-party services might not have native support for monorepos.
• Resolution: Choose tools that explicitly support monorepo workflows. Many modern CI/CD systems and version control platforms provide features tailored for monorepos.

6. Collaboration and Communication:

• Challenge: As the codebase grows, coordinating changes and communicating effectively across teams can become challenging.
• Resolution: Encourage well-defined APIs between projects, maintain clear documentation, and establish communication channels, such as regular meetings or communication platforms, to facilitate collaboration.

7. Developer Onboarding:

• Challenge: New developers might find it overwhelming to navigate and understand a large monorepo.
• Resolution: Provide comprehensive documentation, establish coding standards, and conduct onboarding sessions. Consider creating tools or scripts to automate common tasks and provide a smoother onboarding experience.

8. Versioning and Release Management:

• Challenge: Coordinating versioning and releases across multiple projects can be complex.
• Resolution: Implement a versioning strategy that aligns with your release management process. Tools like Lerna can assist in managing versioning and releases within a monorepo.

9. Security Concerns:

• Challenge: Security vulnerabilities in one project can potentially affect the entire monorepo.
• Resolution: Regularly audit dependencies, apply security patches promptly, and enforce security best practices. Utilize automated security scanning tools to identify vulnerabilities.

10. Branching Strategies:

• Challenge: Choosing an effective branching strategy can be challenging in a monorepo context.
• Resolution: Explore branching models such as trunk-based development or Gitflow. Define clear guidelines for branching and merging to maintain stability and facilitate collaboration.

In summary, while monorepos offer several advantages, they might not be suitable for every project. The decision should be based on the specific needs and characteristics of your development environment and workflow.