Last modified: January 04, 2021

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Mono and multirepo

When managing software projects, organizations often need to choose between two distinct codebase structuring strategies: monorepos and multirepos. This decision isn’t just about where code lives—it affects collaboration, tooling, versioning, and even deployment practices. When you’re starting out or scaling up, it’s important to understand the strengths and trade-offs of each strategy so you can decide what fits your team and project needs.

A monorepo consolidates all projects, applications, libraries, and services into a single repository. This setup encourages centralized collaboration and simplifies dependency management, making it easier for large teams working on tightly coupled, interconnected components. With a monorepo, every change is tracked in one place, and unified versioning is simpler to enforce. For example, you might run a command like this to view the structure of a monorepo:

$ tree -L 2
.
├── apps
│   ├── app1
│   └── app2
├── libs
│   ├── lib1
│   └── lib2
└── services
    ├── service1
    └── service2

The output above shows a clear hierarchy where all code is under one roof. This structure makes it easier to coordinate changes across projects and maintain consistency across shared components. However, it can also mean that even small changes may impact unrelated projects, so strict testing and integration practices become essential.

On the other hand, a multirepo strategy divides each project or component into its own repository. This separation gives teams greater autonomy; each team can work independently, adopt different technologies, and maintain tailored workflows that suit their part of the system. Modular architectures especially benefit from this setup. An example of what the repository layout might look like is:

$ ls
app1/  app2/  lib1/  service1/

Here, each directory is a standalone repository. This separation can lead to faster performance on version control operations and provides flexibility to deploy and scale components independently. It also reduces the complexity inherent in managing a very large codebase, as changes are isolated to specific repositories. Of course, this approach requires robust inter-repository coordination, as dependencies and shared code need to be managed separately.

Monorepos

A monorepo is a single repository that contains all the code for a project—even if that project consists of multiple applications, libraries, or services. This structure is particularly well-suited to large, monolithic codebases and teams requiring close collaboration and frequent code reuse.

+---------------------------------------+
|                                       |
|             MONOREPO                  |
|                                       |
|  +-------+   +-------+   +-------+    |
|  | Proj1 |   | Proj2 |   | Proj3 |    |
|  +-------+   +-------+   +-------+    |
|                                       |
|  Shared Libraries & Dependencies      |
|                                       |
+---------------------------------------+

Advantages

I. Centralized Collaboration

• All code resides in one location, making it easy for developers to find, review, and reuse components.
• Facilitates uniform coding standards and promotes better knowledge-sharing among team members.

II. Unified Dependency Management

• Shared libraries and frameworks reside within the same repository, so any updates affect all dependent projects simultaneously.
• Eliminates the need to synchronize versions of shared libraries across multiple repositories, reducing the risk of version drift.

III. Streamlined Refactoring

• Global changes (e.g., a refactor of a shared library) can be carried out in one atomic commit.
• Ensures consistency and visibility into potential side effects across the entire codebase.

IV. Optimized Build and Test Pipelines

• Centralizing code in a single repository can allow for optimized CI/CD flows (e.g., partial or selective builds for changed components).
• Potentially reduces duplication of test infrastructure and consolidates build artifacts.

V. Atomic Commits

• Large-scale or cross-cutting changes can be made in a single commit, reducing the risk of partial or incomplete updates.
• Ensures other team members can pull the latest changes without encountering partially broken code in separate repositories.

Disadvantages

I. Repository Size and Performance

• As the project grows, Git operations like cloning, fetching, or checking out branches can become slower.
• Developers not needing all sub-projects might be forced to download a large amount of unnecessary data.

II. Branching Complexity

• Many parallel features in one repository can lead to complex branching structures and merge conflicts.
• Teams must coordinate carefully to avoid interfering with each other’s work.

III. Potential for Tight Coupling

• Easy sharing of code can inadvertently introduce hidden dependencies, making it harder to decouple modules later.
• Over time, the codebase may become more “monolithic” if not actively managed.

IV. Steep Onboarding Curve

• New contributors may struggle with the sheer size and scope of a monorepo, slowing their initial productivity.
• Requires clear documentation and a well-structured project layout to avoid confusion.

V. Complex CI/CD Configuration

• Large codebases might need more advanced continuous integration setups to handle partial builds, caching, and test segmentations efficiently.
• Ensuring only the affected components are built/tested can be challenging but is crucial to prevent excessively long pipelines.

VI. Risk of Force Pushes

• A mistaken force push can have a major impact because it affects every piece of the project in the monorepo.
• Strict policies and permissions are usually required to mitigate this risk.

When to Use

• Ideal when a single team (or multiple tightly coordinated teams) needs to work on a shared codebase with frequent cross-project changes.
• Best for monolithic or near-monolithic applications where most modules depend on each other and require synchronized updates.
• If the code in different components changes in tandem, a monorepo simplifies versioning and coordination.

Multirepos

A multirepo approach utilizes separate repositories for each project or component. Each repository contains its own code, dependencies, and versioning history. This strategy is often preferred for service-oriented architectures or projects comprising relatively independent modules.

+-------+   +-------+   +-------+
|       |   |       |   |       |
| Repo1 |   | Repo2 |   | Repo3 |
|       |   |       |   |       |
| Proj1 |   | Proj2 |   | Proj3 |
|       |   |       |   |       |
+-------+   +-------+   +-------+

+--------------------------------------+
|   Shared Libraries & Dependencies    |
+--------------------------------------+

Advantages

I. Clear Independent Versioning

• Each repository manages its own versioning, allowing you to release and update components at different cadences.
• Reduces the chance of unintended breakage if an update is pushed to a shared library that other services are not ready to adopt.

II. Improved Git Performance

• Cloning and pulling updates for smaller, dedicated repositories is generally faster.
• Developers only download and manage the code relevant to their specific service or component.

III. Team Autonomy

• Different teams can choose their own development practices, branching strategies, and release schedules without impacting others.
• Encourages a microservices-like approach where each service can evolve and scale independently.

IV. Greater Flexibility

• Easier to experiment with different technologies or libraries in certain projects without affecting the entire system.
• Projects can be open-sourced individually or shared with external stakeholders without exposing the entire internal codebase.

Disadvantages

I. Challenging Dependency Coordination

• Keeping shared libraries consistent across multiple repositories can become cumbersome.
• Requires clear strategies for updating shared code or libraries across all projects to avoid version mismatches.

II. Risk of Siloed Development

• Different teams may become too isolated, potentially duplicating code or reinventing solutions.
• Communication and collaboration require more effort to ensure alignment across repositories.

III. Harder Code Reuse

• Sharing utilities or libraries involves publishing them to a package repository (e.g., npm, Maven, PyPI) or using Git submodules/subtrees, adding extra overhead.
• Delays can arise if updates to shared code must be published and then adopted by each consumer repository.

IV. Complex Deployment Orchestration

• Deploying changes that span multiple services can be more complicated, often requiring orchestration tools or pipelines.
• Synchronizing releases across multiple repositories demands careful planning and communication.

When to Use

• Modular Projects with Independent Services
  Works best when each service or component can function on its own, with minimal direct dependencies.
• Diverse Teams and Technologies
  If different teams are responsible for distinct parts of the system, possibly using varied tech stacks, multiple repositories can enable more autonomy.
• Frequent, Isolated Releases

Ideal if each service or component has its own release cycle, reducing the need for a single repository to coordinate all updates.