Monorepo vs Polyrepo in Large Systems
Introduction
Repository strategy shapes build performance, developer workflow, and release governance. Large organizations must choose between monorepo and polyrepo based on scaling needs, dependency management, and CI/CD throughput.
Comparison Overview
The table below summarizes key trade-offs.
| Dimension | Monorepo | Polyrepo |
|---|---|---|
| Dependency management | Centralized, easier to refactor | Decentralized, versioned contracts |
| CI complexity | Requires selective builds | Simpler per repo but more pipelines |
| Access control | Harder to isolate by repo | Easier to isolate per service |
| Tooling | Strong tooling required (build graph, caching) | Standard tooling per repo |
| Change coordination | Single PR can change many services | Cross-repo changes require orchestration |
CI/CD Implications
Monorepos demand build graph awareness and test selection. Without that, CI scales linearly with repo size and becomes cost-prohibitive. Polyrepos simplify builds but require orchestration for multi-service changes.
Versioning and Contracts
Polyrepos depend on strong versioned contracts. A shared library in a polyrepo model should be treated as a published artifact.
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public class PricingRequest
{
public string Region { get; init; } = string.Empty;
public decimal Amount { get; init; }
}
Publish this contract as a NuGet package, and use semantic versioning to manage compatibility.
When to Choose Monorepo
- Heavy cross-service refactoring is common.
- You can invest in build caching and test selection tooling.
- Organization prefers a single source of truth.
When to Choose Polyrepo
- Teams require isolated ownership and access control.
- Services have independent release cadences.
- Tooling investment is limited or distributed.
Summary
Monorepo and polyrepo both work at scale, but each demands different operational discipline. Choose the model that aligns with your tooling maturity, security needs, and release coordination requirements.