Scalable API Design in Modern .NET Core

Building backend systems that scale requires a strict separation of concerns, optimized data query pipelines, and structured API endpoints. In the modern .NET ecosystem, we can achieve maximum performance by combining clean architecture, Minimal APIs, and advanced SQL features.

Clean Architecture Layers

To make enterprise codebases maintainable, we separate the system into three main layers:

1. Domain Layer: Contains enterprise entities, types, and core business exceptions. It has zero external dependencies.
2. Application Layer: Defines interfaces, models (DTOs), and use-cases. We frequently use the mediator pattern (MediatR) to decouple commands and queries (CQRS).
3. Infrastructure Layer: Handles external integrations, database contexts (Entity Framework Core / Dapper), and file systems.

Embracing Minimal APIs

Introduced in recent versions of .NET, Minimal APIs drastically reduce boilerplate while improving throughput. By registering endpoints directly with the builder:

app.MapGet("/api/v1/orders/{id}", async (Guid id, IMediator mediator) => 
{
    var query = new GetOrderByIdQuery(id);
    var result = await mediator.Send(query);
    return result is not null ? Results.Ok(result) : Results.NotFound();
})
.WithName("GetOrderById")
.WithTags("Orders")
.RequireAuthorization();

This approach bypasses traditional controller overhead, providing a clean entrypoint layer matching the responsiveness expected of modern SaaS backends.