Monorepo vs. multiple repositories: what’s the best strategy for a growing codebase?

Source: Dev.to

The Evolving Challenge of Code Structure

The repository structure that works for a two‑person startup almost never works for a fifty‑person engineering team. What starts as a simple, clean codebase eventually develops friction points as more people and services are added.

The conversation about whether to use a single monorepo or split work across multiple repositories usually starts when:

• Dependency management gets complicated.
• Practices drift between teams.
• CI builds start taking way too long.

It’s a constant tension between giving teams the independence to move fast and maintaining the shared context needed for services to actually work together.

In Practice: The Pain Shows Up in Pull Requests

• A simple bug fix in a shared library requires five separate PRs in five different service repositories.
• A developer on the web team can’t test their changes locally because the API team just refactored a core model, and nobody realized the dependency was there.

These aren’t theoretical problems; they’re daily slowdowns that block releases and frustrate engineers. The core challenge is finding a structure that minimizes coordination overhead without creating new bottlenecks.

Understanding the Core Architectures: Monorepo vs. Multiple Repositories

The debate comes down to two primary models for organizing code. Each optimizes for a different set of priorities and introduces its own specific set of problems when not managed correctly.

The Monorepo Approach: Consolidating Related Code

A monorepo is a single repository containing multiple distinct projects with well‑defined relationships.

Example: A frontend application, its backend API, and a shared component library all living in the same Git repository.

Advantages

• Atomic changes across all projects in a single commit.
• When an API contract changes, you can update the API server and its clients in the same PR, ensuring they stay in sync.
• Enforces consistency with shared tooling (linters, test frameworks, etc.).

Challenges at Scale

• git clone and git status can become slow.
• Build systems must be smart enough to test/deploy only what actually changed, requiring specialized tooling.
• Access control becomes tricky: granting a contractor access to one project may inadvertently give them access to the entire codebase.

The Multiple Repository Approach

Each service, application, or library gets its own repository.

Example: The payments team owns the payments‑api repository.

Advantages

• Clear ownership of each part.
• Teams can develop, test, and deploy on their own schedule.
• Smaller repositories → faster builds.
• Straightforward access control.

Trade‑offs

• Coordination overhead: managing dependencies across dozens of repos is a serious operational burden.
• A change to a common utility library can trigger a cascade of updates, PRs, and deployments across the organization.
• Risk of “version soup” where different services run different versions of the same internal library, making bugs hard to track.
• Enforcing consistent testing, security, and deployment practices requires extra effort because there’s no single source of truth.

Key Factors When Choosing a Repository Strategy

The right choice depends entirely on your context. Look at how your code, teams, and processes actually work—not at trends. Four factors tend to matter most.

1. Interdependencies and Coupling

• How often do components need to change together?
  • If your frontend and backend are almost always deployed in lockstep, separating them creates constant, unnecessary work.
  • Coordinating PRs and managing versions becomes a direct tax on developer productivity.
• If services are truly independent and interact through stable, versioned APIs, multiple repositories might work just fine.

2. Team Structure and Collaboration Patterns

• Small, co‑located teams can easily manage the communication overhead of a monorepo.
• Large, distributed organizations (different time zones) benefit from the clear ownership lines of multiple repositories, reducing communication friction.
• Decide whether you want to optimize for clear boundaries & asynchronous work (multi‑repo) or seamless cross‑team refactoring & shared context (monorepo).

3. Build, Test, and Deployment Workflows

• Monorepo: Requires an intelligent build system that can identify the subset of the codebase affected by a change and run only the relevant tests and deployments. Without this, CI times become a bottleneck.
• Multi‑repo: Needs standardized CI/CD pipelines that can be applied across all repositories, plus a strategy for orchestrating releases that involve changes to multiple services (e.g., rolling out a change that requires both an API and a web app to be updated simultaneously).

4. Tooling Ecosystem and Infrastructure

• Modern tools like Bazel, Nx, and Turborepo make monorepos much more viable by handling task scheduling and remote caching, allowing huge codebases to stay fast.
• Adopting a monorepo without investing in this tooling is a recipe for failure.

Bottom Line

There is no one‑size‑fits‑all answer. Evaluate the four factors above in the context of your organization, and choose the repository strategy that aligns with your productivity goals, team dynamics, and infrastructure capabilities.

A Framework for Evaluation

Instead of looking for a universally correct answer, evaluate your specific situation. The best strategy is the one that causes the least amount of friction for your team’s day‑to‑day work.

Assessing Your Current State and Future Needs

1. Analyze code‑base interconnectedness

   • Review recent PRs and feature development cycles.
   • How many required changes in more than one service or library?
   • A high number signals that the coordination overhead of a multi‑repo setup is already costing you.

2. Consider team structure

   • Are you organized into small, autonomous product teams?
   • Or is there a lot of cross‑team collaboration?

3. Evaluate operational overhead

   • Do you have platform‑engineering resources to build and maintain the specialized tooling a monorepo requires?
   • Or do you have the capacity to standardize processes across many repositories?

What to Consider for a Monorepo to Work Well

If you decide a monorepo is the right fit, success depends on a few key practices:

1. Invest in Tooling from Day One

• Use robust build, test, and code‑navigation tools.
• Don’t assume you can just put everything in one folder and figure it out later.
• CI optimization: Apply path‑based filtering so that a change to documentation doesn’t trigger the entire backend test suite.

2. Define Clear Responsibilities

• Add CODEOWNERS files to specify which teams own which parts of the codebase.
• This routes PRs to the right people and prevents code from becoming orphaned.

# Example CODEOWNERS
/docs/       @docs-team
/backend/    @backend-team
/frontend/   @frontend-team

3. Make It Easy to Find Code and Manage Versions

• Provide a clear strategy for versioning internal libraries within the monorepo to manage breaking changes.
• Offer discoverability tools (e.g., searchable index, package manifests) so developers can quickly locate shared code.

What to Consider When Managing Multiple Repositories

If you’re operating a multi‑repo setup, discipline and standardization are critical.

1. Standardize Everything You Can

• Create templates or “starter kits” for new services that include:

  • Standardized build scripts
  • Dockerfiles
  • Linting configurations
  • CI/CD pipelines

• This prevents configuration drift and makes it easier for developers to move between projects.

2. Be Disciplined About Versioning

• Use semantic versioning for all shared libraries and APIs.
• Automate dependency updates (e.g., Dependabot) to avoid falling behind on security patches and bug fixes.

3. Define Clear Boundaries and API Contracts

• When services live in separate repositories, their APIs become the only formal contract between them.
• Ensure APIs are:
  • Well‑documented
  • Stable
  • Backward‑compatible

Re‑Evaluating Your Strategy: When and How

Your repository choice is not permanent. Periodically re‑evaluate whether the current strategy still serves you well.

Warning Signs

• Recurring, painful friction (e.g., cross‑cutting changes taking weeks across repos).
• Teams blocked waiting for another team to release a new library version.
• Monorepo build times so slow developers avoid running tests.

Incremental Adjustments Before a Large‑Scale Migration

1. Identify tightly coupled services that always change together.
2. Merge only those into a single monorepo and observe friction reduction.
3. Iterate: Continue adjusting code organization to match how teams and systems actually work, rather than chasing an architectural ideal.