Minimal APIs vs Controllers

var builder = WebApplication.CreateBuilder(args);

// Core services
builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

// Application services
builder.Services.AddScoped<IOrderRepository, OrderRepository>();
builder.Services.AddScoped<IOrderValidator, OrderValidator>();
builder.Services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();

var app = builder.Build();

[ApiController]
[Route("api/v1/orders")]
public class OrdersController : ControllerBase
{
    private readonly IOrderRepository _repo;
    private readonly IOrderValidator _validator;

    public OrdersController(IOrderRepository repo, IOrderValidator validator)
    {
        _repo = repo;
        _validator = validator;
    }

    [HttpPost]
    [ProducesResponseType(StatusCodes.Status201Created)]
    [ProducesResponseType(StatusCodes.Status400BadRequest)]
    public async Task<IActionResult> CreateOrder([FromBody] CreateOrderRequest request)
    {
        var validationResult = await _validator.ValidateAsync(request);
        if (!validationResult.IsValid)
            return BadRequest(validationResult.Errors);

        var order = await _repo.CreateAsync(request);
        return CreatedAtAction(nameof(GetOrder), new { id = order.Id }, order);
    }

    [HttpGet("{id:guid}")]
    [ProducesResponseType(StatusCodes.Status200OK)]
    [ProducesResponseType(StatusCodes.Status404NotFound)]
    public async Task<IActionResult> GetOrder(Guid id)
    {
        var order = await _repo.GetByIdAsync(id);
        return order is null ? NotFound() : Ok(order);
    }
}

app.MapPost("/api/v1/orders", async (
    CreateOrderRequest request,
    IOrderRe

pository repo, IOrderValidator validator) => { var validationResult = await validator.ValidateAsync(request); if (!validationResult.IsValid) return Results.BadRequest(validationResult.Errors);

var order = await repo.CreateAsync(request);
return Results.Created($"/api/v1/orders/{order.Id}", order);

}).WithName("CreateOrder").WithOpenApi();

app.MapGet("/api/v1/orders/{id:guid}", async ( Guid id, IOrderRepository repo) => { var order = await repo.GetByIdAsync(id); return order is null ? Results.NotFound() : Results.Ok(order); }).WithName("GetOrder").WithOpenApi();

### Step 4: Middleware & Global Error Handling
Both approaches benefit from centralized error handling. Register middleware before routing to catch unhandled exceptions.

```csharp
app.UseExceptionHandler(errorApp =>
{
    errorApp.Run(async context =>
    {
        context.Response.StatusCode = StatusCodes.Status500InternalServerError;
        context.Response.ContentType = "application/json";

        var exceptionHandlerFeature = context.Features.Get<IExceptionHandlerFeature>();
        var error = new { Message = "Internal server error", Detail = exceptionHandlerFeature?.Error.Message };
        await JsonSerializer.SerializeAsync(context.Response.Body, error);
    });
});

app.UseRouting();
app.UseAuthentication();
app.UseAuthorization();

Architecture Decisions & Rationale

• Routing: Controllers use attribute routing, enabling explicit URL contracts and versioning strategies. Minimal APIs use path-based registration, which is faster to write but harder to refactor when endpoints multiply.
• DI Integration: Controllers resolve dependencies via constructor injection, guaranteeing lifecycle consistency. Minimal APIs resolve dependencies via method parameters, which delegates to HttpContext.RequestServices. This works but requires careful attention to scoped vs singleton lifetimes.
• Validation: Controllers integrate with ModelState and action filters. Minimal APIs require manual validation calls or custom endpoint filters. Production systems should standardize on FluentValidation or DataAnnotations regardless of approach.
• OpenAPI: Controllers generate metadata automatically. Minimal APIs require .WithOpenApi() and explicit ProducesResponseType equivalents via .Produces<T>() or custom OpenApiOperation builders.

Pitfall Guide

1. Treating Minimal APIs as a monolith replacement Minimal APIs lack structural boundaries. When 30+ endpoints share a single Program.cs or scattered RouteGroup files, navigation, code review, and merge conflicts become unmanageable. Controllers enforce file-per-resource conventions that scale with team size.

2. Ignoring DI scope resolution in minimal endpoints Parameter injection in minimal APIs uses HttpContext.RequestServices. If you resolve a scoped service inside a singleton delegate or cache the delegate, you'll encounter disposed context exceptions or stale data. Always resolve per-request or use IServiceProvider explicitly within the delegate.

3. Overusing inline delegates instead of extracting handlers Writing business logic directly in MapGet/MapPost creates untestable, unmockable code. Extract to handler classes or static methods. Minimal APIs should delegate to application layer classes, just like controllers.

4. Assuming controllers are inherently slower in steady state Reflection-based controller discovery happens once during startup. After warmup, routing uses compiled expression trees and action descriptors. The runtime performance difference is <0.05ms per request. Optimizing for cold-start at the expense of maintainability is a misallocation of engineering effort.

5. Neglecting OpenAPI/Swagger configuration differences Controllers generate endpoints automatically. Minimal APIs require explicit .WithOpenApi() and metadata configuration. Forgetting this breaks client SDK generation and API documentation. Standardize on a source generator or endpoint metadata convention to avoid drift.

6. Mixing patterns without architectural boundaries Using controllers for admin endpoints and minimal APIs for public APIs in the same project creates inconsistent error handling, validation pipelines, and testing strategies. Choose one pattern per bounded context, or isolate them in separate projects/assemblies.

7. Skipping validation/error handling middleware Both approaches default to returning raw exceptions or inconsistent JSON shapes. Production systems must implement global exception handling, standardized error responses (ProblemDetails), and validation middleware. Neither pattern provides this out of the box.

Best Practices from Production

• Use vertical slice architecture: group by feature, not by layer. This works identically for both approaches.
• Standardize on ProblemDetails for error responses. Configure Microsoft.AspNetCore.Mvc.ProblemDetails in Program.cs.
• Extract all business logic to application handlers. Controllers and minimal endpoints should only handle HTTP concerns.
• Use RouteGroupBuilder to namespace minimal APIs. It provides prefix routing, shared metadata, and filter pipelines.
• Measure routing performance only after JIT warmup. Cold-start metrics are irrelevant for containerized deployments with health checks and pre-warm strategies.

Production Bundle

Action Checklist

• Define architectural boundary: choose one pattern per bounded context or project
• Configure global error handling using UseExceptionHandler and ProblemDetails
• Standardize validation: integrate FluentValidation or DataAnnotations consistently
• Extract business logic to handler classes; keep endpoints thin
• Wire OpenAPI/Swagger with explicit metadata for minimal APIs or controller attributes
• Implement integration tests using WebApplicationFactory for both patterns
• Set up route versioning strategy (/api/v1/, /api/v2/) before scaling endpoints
• Benchmark routing latency after JIT warmup, not during cold start

Decision Matrix

Scenario	Recommended Approach	Why	Cost Impact
Microservice with <10 endpoints, single developer	Minimal APIs	Low ceremony, rapid iteration, reduced boilerplate	Lower initial dev cost, higher refactoring cost if scope expands
Enterprise monolith, 3+ teams, complex domain	Controllers	Explicit routing, mature testing, predictable DI lifecycle	Higher initial setup cost, lower long-term maintenance cost
Rapid prototype or internal tooling	Minimal APIs	Fastest path to working HTTP surface, minimal configuration	Near-zero setup cost, technical debt accumulates if promoted to production
Team with ASP.NET MVC/Web API background	Controllers	Familiar patterns, reduced onboarding friction, existing skill leverage	Zero retraining cost, faster feature delivery

Configuration Template

// Program.cs - Production-ready baseline
var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers()
    .AddJsonOptions(opts => opts.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase);
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen(c => c.CustomSchemaIds(t => t.FullName));

// Validation
builder.Services.AddScoped(typeof(IValidator<>), typeof(Validator<>));

// Repositories & Handlers
builder.Services.AddScoped<IOrderRepository, OrderRepository>();
builder.Services.AddScoped<CreateOrderHandler>();

// Global error handling
builder.Services.AddProblemDetails();

var app = builder.Build();

app.UseExceptionHandler();
app.UseSwagger();
app.UseSwaggerUI();

app.UseRouting();
app.UseAuthentication();
app.UseAuthorization();

// Controllers
app.MapControllers();

// Minimal APIs (if used)
var orders = app.MapGroup("/api/v1/orders");
orders.MapPost("/", async (CreateOrderRequest req, CreateOrderHandler handler) =>
{
    var result = await handler.ExecuteAsync(req);
    return Results.Created($"/api/v1/orders/{result.Id}", result);
}).WithName("CreateOrder").WithOpenApi();

app.Run();

Quick Start Guide

1. Create a new project: dotnet new web -n ApiArchitecture && cd ApiArchitecture
2. Add dependencies: dotnet add package Microsoft.AspNetCore.OpenApi && dotnet add package Swashbuckle.AspNetCore
3. Replace Program.cs with the Configuration Template above, adjust service registrations to match your domain
4. Run: dotnet run and navigate to /swagger to verify endpoints, validation, and error handling are operational

This setup compiles, configures DI, wires OpenAPI, and provides both controller and minimal API registration points. From here, extract handlers, add integration tests, and enforce architectural boundaries per bounded context. The choice between Minimal APIs and Controllers is not a performance optimization; it is a structural contract. Align it with team size, domain complexity, and long-term maintenance expectations.