Monorepo — A Concept Summary

Restored from a 2020-05 archive. Lerna was the default choice then; today pnpm workspaces and Turborepo are more common.

I recently started a module project built on the monorepo concept, so I'm revisiting monorepo fundamentals in this post.

Until now I only had a basic conceptual understanding — I hadn't had much chance to try it in a real project. I'd been developing NPM modules with the classic multi-repo approach: one repository per module.

Then a new project came up that adopted Lerna as a version management tool, which gave me a reason to organize my thinking about monorepos again.

In one sentence: a monorepo puts what was managed as multiple repositories into a single repository. The opposite is a multi-repo.

Monorepo vs Multi-Repo

Type	Definition
Monorepo	Manage multiple logical repositories inside one physical repository
Multi-Repo	Each package lives in its own repository

Monorepo Advantages

• Easier management from a single repo
• Simpler code reuse
• Lower overhead for dependency management
• Easier dev environment setup, build, and test
• Cross-project integration tests and code search become straightforward
• A single commit can refactor an API and all its callers
• Makes large-scale refactoring feasible
• Smoother collaboration across teams

Monorepo Disadvantages

• Need mechanisms for tracking up-to-date dependencies
• Version information can be lost
• Weaker per-project isolation boundaries
• Requires more storage