Vertical Slices Architecture

Vertical Slices Architecture

Understanding Vertical Slices Architecture: A Modern Approach to Scalable Software Design

In the ever-evolving landscape of software development, developers continually seek better ways to build systems that are modular, maintainable, and scalable. One such approach that has gained traction in recent years is Vertical Slices Architecture. Unlike the traditional layered (or n-tier) architecture, vertical slices offer a fresh perspective by organizing code around features rather than technical layers.

In this article, we will explore what vertical slices architecture is, why it's useful, how it compares to traditional architectures, and how to implement it effectively.

What Is Vertical Slices Architecture?

Vertical Slices Architecture is a design paradigm where each slice of the application represents a complete feature or behavior, encompassing all the layers required to fulfill a user request — from the API layer, through the business logic, down to the data access layer.

Think of it as designing your application around use cases or user stories, where each slice is self-contained and independently deployable, testable, and understandable.

Example

Instead of organizing your code like this:

- Controllers/

- Services/

- Repositories/

- Models/

You would structure it by feature:

- Features/

    - Users/

        - CreateUser.cs

        - GetUserById.cs

        - UpdateUser.cs

    - Products/

        - AddProduct.cs

        - ListProducts.cs

Key Characteristics

  • Feature-Oriented: Code is organized by what it does rather than how it does it.
  • Isolation: Each slice can be modified with minimal impact on others.
  • Simplicity: Reduced indirection compared to layered architectures.
  • Testability: Easier to write focused tests for individual features.
  • Scalability: Teams can work independently on different features.

Vertical Slices vs Layered Architecture

Aspect Layered Architecture Vertical Slices Architecture
Organization Technical layers (UI, BLL, DAL) Feature/use-case-based
Coupling Higher due to shared services Lower due to encapsulated features
Readability Requires tracing through layers Self-contained, easier to follow
Modifiability Risk of breaking shared components Safe to change individual slices
Testing Often requires integration tests Encourages focused unit testing

When Should You Use Vertical Slices?

Vertical Slices Architecture is especially effective in the following scenarios:

  • Building modular monoliths or microservices
  • Projects with a large number of independent features
  • Systems where fast iteration and isolated changes are a priority
  • Teams that value clear boundaries and responsibilities

How to Implement Vertical Slices

  1. Define Your Use Cases: Start with identifying the key operations your system needs.
  2. Create Feature Folders: Organize files (commands, queries, handlers, models) around these use cases.
  3. Use Mediator Pattern (Optional): Libraries like MediatR can help decouple components further.
  4. Limit Cross-Slice Dependencies: Ensure each slice remains as self-contained as possible.
  5. Test per Slice: Write unit and integration tests within the feature folder.

Example Using MediatR in .NET



// CreateUser.cs

public record CreateUserCommand(string Name, string Email) : IRequest<Guid>;

public class CreateUserHandler : IRequestHandler<CreateUserCommand, Guid>

{

    public async Task<Guid> Handle(CreateUserCommand request, CancellationToken cancellationToken)

    {

        var user = new User { Name = request.Name, Email = request.Email };

        // Save to database

        return user.Id;

    }

}

Benefits of Vertical Slices

  • Faster onboarding: New developers can understand one slice without understanding the whole system.
  • Less regression risk: Changes are isolated, reducing the chance of side effects.
  • Improved modularity: Makes eventual migration to microservices easier.
  • Better DDD alignment: Encourages domain-driven design by keeping related logic together.

Challenges to Consider

  • Initial learning curve: Developers used to layered approaches may need time to adjust.
  • Overhead in small apps: The feature-based structure may feel heavy for tiny projects.
  • Consistency: Teams need discipline to maintain consistent folder and naming conventions.

Conclusion

Vertical Slices Architecture offers a pragmatic, scalable way to build modern software systems. By organizing code around features rather than layers, it enhances modularity, testability, and maintainability. Whether you are working on a monolith or microservices, adopting vertical slices can lead to cleaner, more robust code and a happier development team.

Further Reading:

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