The term "Monorepo" is a compound of two words: "Mono," meaning single, and "Repo," short for repository. In the context of DevOps, a monorepo refers to a software development strategy where code for many projects is stored in the same repository. This approach contrasts with the more traditional multi-repo strategy, where each project has its own repository.
Monorepos have been a topic of intense debate within the DevOps community. Supporters argue that they simplify dependency management and make cross-project changes easier. Critics, on the other hand, point to potential problems with codebase size, difficulty in understanding the impact of changes, and challenges in access control and code ownership.
Definition and Explanation of Monorepo
A monorepo is a single repository that stores all of a company's deliverable code and assets. This includes all libraries, services, applications, and configurations. The monorepo approach is not tied to a specific technology or language; it can be used with any version control system and any programming language.
Monorepos can be thought of as a centralized system for managing code. All developers pull from and push to the same repository, and there is a single source of truth for all code and assets. This can simplify many aspects of software development, but it also introduces new challenges and complexities.
Advantages of Monorepo
One of the main advantages of a monorepo is simplified dependency management. With all code in the same place, it's easy to ensure that all projects are using the same versions of libraries and other dependencies. This can prevent "dependency hell," where different projects require incompatible versions of the same library.
Another advantage of a monorepo is that it can make cross-project changes easier. If a change needs to be made to a library that is used by multiple projects, it can be made once in the monorepo, and all projects will get the updated version. In a multi-repo setup, this would require coordinating changes across multiple repositories.
Disadvantages of Monorepo
One of the main criticisms of monorepos is that they can become very large, which can slow down operations like cloning, pulling, and pushing. This can be mitigated with techniques like sparse checkouts, where only a subset of the repository is checked out, but this adds complexity.
Another criticism of monorepos is that they can make it difficult to understand the impact of changes. With so much code in one place, a change to a single line of code could potentially impact any project in the repository. This can make testing and validation more challenging.
History of Monorepo
The monorepo approach is not new; it has been used by large tech companies like Google and Facebook for many years. Google's monorepo, known as "Piper," contains over 2 billion lines of code and is used by more than 25,000 developers.
Facebook also uses a monorepo for its code, and has developed tools like Buck and Phabricator to help manage it. These tools have been open-sourced, allowing other companies to benefit from Facebook's experience with monorepos.
Monorepo in Open Source
Monorepos are also becoming more popular in the open source community. Projects like Babel, React, and Angular all use monorepos. These projects have found that monorepos make it easier to coordinate changes across multiple packages, and simplify the process of contributing to the project.
However, using a monorepo in an open source project can also present challenges. It can be more difficult to manage access control, as all contributors have access to all code. It can also be harder to track issues and pull requests, as they are all in the same place.
Use Cases for Monorepo
Monorepos can be a good fit for large, complex projects where there is a lot of interdependency between components. They can also be beneficial for projects that need to enforce consistency across multiple packages, as they make it easier to ensure that all packages are using the same versions of dependencies.
However, monorepos may not be the best choice for all projects. Small, independent projects may not benefit from a monorepo, and may find it adds unnecessary complexity. Similarly, projects that need to maintain strict access control or separation of concerns may be better served by a multi-repo approach.
Monorepo in Large Organizations
Large organizations often find that a monorepo approach simplifies their development process. With all code in one place, it's easier to coordinate changes across multiple teams and projects. It's also easier to enforce coding standards and best practices, as there is a single source of truth for all code.
However, large organizations also need to be aware of the potential challenges of a monorepo. These include managing the size of the repository, understanding the impact of changes, and maintaining access control and code ownership.
Monorepo in Small Teams
Small teams can also benefit from a monorepo, especially if they are working on a complex project with many interdependencies. A monorepo can simplify dependency management and make it easier to coordinate changes.
However, small teams also need to be aware of the potential downsides of a monorepo. These include the complexity of managing a large repository, and the potential difficulty of understanding the impact of changes.
Examples of Monorepo
Google and Facebook are two of the most well-known examples of companies using a monorepo. Google's monorepo, Piper, contains over 2 billion lines of code and is used by more than 25,000 developers. Facebook's monorepo includes all of the company's code, and the company has developed tools like Buck and Phabricator to help manage it.
In the open source community, projects like Babel, React, and Angular all use monorepos. These projects have found that a monorepo makes it easier to coordinate changes across multiple packages, and simplifies the process of contributing to the project.
Google's Monorepo
Google's monorepo, Piper, is one of the largest in the world. It contains over 2 billion lines of code and is used by more than 25,000 developers. Google has developed a number of tools to help manage Piper, including a custom version control system called CitC (Client in the Cloud).
Piper allows Google to enforce consistency across all of its projects, and makes it easier to coordinate changes across multiple teams and projects. However, managing such a large repository also presents challenges, and Google has had to develop sophisticated tooling to handle these.
Facebook's Monorepo
Facebook also uses a monorepo for all of its code. The company has developed tools like Buck, a build system that allows for fast, incremental builds, and Phabricator, a suite of tools for code review and project management.
Facebook's monorepo allows the company to ensure that all of its projects are using the same versions of dependencies, and makes it easier to coordinate changes across multiple projects. However, like Google, Facebook has had to develop sophisticated tooling to manage its monorepo.
Conclusion
Monorepos are a powerful tool for managing code in large, complex projects. They simplify dependency management, make it easier to coordinate changes across multiple projects, and provide a single source of truth for all code. However, they also present challenges, including managing the size of the repository, understanding the impact of changes, and maintaining access control and code ownership.
Whether a monorepo is the right choice for a project depends on the specific needs and circumstances of the project. Large organizations with many interdependent projects may find that a monorepo simplifies their development process, while smaller, independent projects may find that a monorepo adds unnecessary complexity.