In modern software development, the structure and organization of code repositories are critical to project maintainability, scalability, and collaboration. The decision between using a Polyrepo, Monorepo, or Modular Monolith impacts how teams manage code, handle dependencies, maintain CI/CD pipelines, and collaborate on development efforts. Given the project’s requirements, this decision is critical to balancing scalability, development velocity, and maintainability.
Driving Factors
Scalability
Can the repository structure scale as the codebase grows?
Maintainability
How easy is it to manage, update, and refactor?
Development Workflow
How does the structure affect collaboration, code owners, branching strategies, and developer workflows?
CI/CD Complexity
How does the repository strategy affect build times, release, and deployment pipelines?
Dependency Management
How efficiently can internal and external dependencies be managed?
3. Decision
NOTE The decision should be reviewed periodically, particularly if the project significantly scales in team size or service complexity. Transitioning to a Polyrepo architecture or evolving towards microservices may be reconsidered if necessary.
Modular Monolith
Evaluating the project’s current size, team structure, growth potential, and operational requirements, the Modular Monolith option is selected. The decision balances the simplicity of a monolithic codebase with the architectural benefits of modularization. This approach ensures that teams can maintain independence between modules while still benefiting from a single source of truth.
4. Considered
Polyrepo (Multiple Repositories)
In a polyrepo strategy, each service, module, library, or component is maintained in its own repository. This creates clear boundaries between services or modules, giving teams greater autonomy.
Pros
Isolation of Services/Components
Clear separation between modules, enabling independent versioning, CI/CD pipelines, and deployments.
Team Autonomy
Teams can work on isolated codebases with their own processes and policies without impacting others.
Granular Access Control
Teams can limit access to specific repositories, improving security and compartmentalization.
Scalability
Allows distributed teams to scale independently, without affecting other parts of the system.
Cons
Dependency Management Complexity
Managing cross-repository dependencies can become complex, requiring custom tooling or significant configuration.
Overhead of Versioning
Synchronizing version upgrades across multiple repos can introduce additional complexity.
Coordination Overhead
Coordinating changes across multiple repositories can lead to overhead, particularly for large-scale refactorings or integration tests.
Inconsistent Practices
Risk of divergent practices across repositories, making consistency harder to enforce.
Monorepo (Single Repository)
A monorepo approach consolidates all services, modules, libraries, and components into a single repository. The entire codebase is versioned together, and all parts of the system are developed and maintained centrally.
Pros
Unified Codebase
Simplifies dependency management, as all code is within a single repo, enabling easy sharing and updating of libraries.
Simplified Dependency Management
Internal dependencies can be handled with easier as the whole codebase shares a single source of truth.
Collaboration Efficiency
Facilitates easier coordination between teams working on interconnected services or components.
Atomic Changes
Cross-project changes can be implemented atomically in a single commit, reducing inconsistencies, reducing integration challenges and minimizing version mismatches.
Cons
Scaling Complexity
The larger the codebase, the more difficult it can become to manage the repository in terms of performance, especially with large commit histories or complex branching strategies.
Reduced Autonomy
Teams lose some autonomy, as changes in one area of the codebase might affect others, requiring greater coordination.
Performance Bottlenecks
Potential performance bottlenecks (e.g. Git) and tooling complexity as the codebase scales.
Modular Monolith (Single Repository with Modular Architecture)
The codebase resides in a single repository but is structured into well-defined, independent modules or components that can function as individual units with strong boundaries while adhering to a monolithic strategy.
Pros
Modularity
Provides the benefits of both modularity (encapsulation) and simplicity (single repository).
Simplified Refactoring
Allows for system-wide refactorings without the overhead of managing multiple repositories.
Consistency
Ensures consistent practices across teams while avoiding the scaling challenges of a pure monolith.
Simplified Dependencies
Sharing code and dependencies across modules is straightforward, reducing the overhead of managing external repositories.
Cons
Deployment Bottlenecks
The entire monolithic system must be deployed as a whole, which can delay the release of independent modules.
Module Overhead
As the system grows, the boundaries between modules must be carefully maintained to avoid creating a large, tangled codebase.
Scaling Complexity
For large-scale applications, the performance overhead of a single repository may become problematic, especially if CI/CD pipelines struggle with the build process.
5. Consequences
Polyrepo
Greater complexity in dependency management and coordination between repositories.
Teams must invest in strong versioning and integration strategies.
Monorepo
Potential performance bottlenecks and tooling complexity as the codebase scales.
Streamlined collaboration and simpler dependency management.
Modular Monolith
Balances simplicity with modularity but may introduce deployment challenges.
May require future migration towards Polyrepo if the system grows too large.
XXX-ADR: Repository Strategies
Architectural Decision Records (ADR) for Repository Strategies in Software Develpoment.
1. State
2. Context
In modern software development, the structure and organization of code repositories are critical to project maintainability, scalability, and collaboration. The decision between using a
Polyrepo,Monorepo, orModular Monolithimpacts how teams manage code, handle dependencies, maintain CI/CD pipelines, and collaborate on development efforts. Given the project’s requirements, this decision is critical to balancing scalability, development velocity, and maintainability.Driving Factors
Scalability
Maintainability
Development Workflow
CI/CD Complexity
Dependency Management
3. Decision
Modular Monolith
Evaluating the project’s current size, team structure, growth potential, and operational requirements, the Modular Monolith option is selected. The decision balances the simplicity of a monolithic codebase with the architectural benefits of modularization. This approach ensures that teams can maintain independence between modules while still benefiting from a single source of truth.
4. Considered
Polyrepo (Multiple Repositories)
In a polyrepo strategy, each service, module, library, or component is maintained in its own repository. This creates clear boundaries between services or modules, giving teams greater autonomy.
Pros
Isolation of Services/Components
Team Autonomy
Granular Access Control
Scalability
Cons
Dependency Management Complexity
Overhead of Versioning
Coordination Overhead
Inconsistent Practices
Monorepo (Single Repository)
A monorepo approach consolidates all services, modules, libraries, and components into a single repository. The entire codebase is versioned together, and all parts of the system are developed and maintained centrally.
Pros
Unified Codebase
Simplified Dependency Management
Collaboration Efficiency
Atomic Changes
Cons
Scaling Complexity
Reduced Autonomy
Performance Bottlenecks
Modular Monolith (Single Repository with Modular Architecture)
The codebase resides in a single repository but is structured into well-defined, independent modules or components that can function as individual units with strong boundaries while adhering to a monolithic strategy.
Pros
Modularity
Simplified Refactoring
Consistency
Simplified Dependencies
Cons
Deployment Bottlenecks
Module Overhead
Scaling Complexity
5. Consequences
Polyrepo
Greater complexity in dependency management and coordination between repositories.
Teams must invest in strong versioning and integration strategies.
Monorepo
Potential performance bottlenecks and tooling complexity as the codebase scales.
Streamlined collaboration and simpler dependency management.
Modular Monolith
Balances simplicity with modularity but may introduce deployment challenges.
May require future migration towards Polyrepo if the system grows too large.