API Versioning in ASP.NET Core

API versioning in ASP.NET Core is a strategy for managing changes to your API over time while maintaining backward compatibility for existing clients. This allows you to introduce new features, modify existing functionality, or restructure your API without breaking applications that rely on older versions.

Why Versioning is Needed

• Backward Compatibility: Ensures that older client applications continue to function correctly even after significant changes are introduced in newer API versions.
• Controlled Evolution: Allows for gradual updates and enhancements to the API, preventing a complete overhaul that could disrupt all clients simultaneously.
• Client Flexibility: Provides clients with the option to upgrade to newer versions at their own pace, rather than being forced to adopt changes immediately.

Common REST API Versioning Strategies

1. URL-based Versioning

The API version is included directly in the URL path (e.g., /api/v1/products, /api/v2/products).

• Format: /api/v1/resource
• Pros: Easy to implement and understand; visible in logs and browser.
• Cons: Can clutter the URI space; not ideal for hypermedia-driven APIs.

2. Header-based Versioning

The API version is sent in a custom request header (e.g., X-API-Version: 1.0).

• Format: Accept: application/vnd.myapi.v1+json
• Pros: Keeps URLs clean; aligns with content negotiation.
• Cons: Harder to test/debug; less visible to consumers.

3. Query Parameter Versioning

The API version is specified as a query parameter (e.g., /api/products?api-version=1.0).

• Format: /api/resource?version=1
• Pros: Simple to implement; flexible.
• Cons: Not RESTful by strict standards; can be overlooked by caching proxies.

4. Custom Request Header

• Format: X-API-Version: 1
• Pros: Clean separation of concerns.
• Cons: Requires clients to explicitly set headers; not self-documenting.

5. Media Type Versioning

The API version is embedded within the Accept header's media type (e.g., Accept: application/vnd.yourcompany.product-v1+json).

Implementation Steps in ASP.NET Core

• Install the Microsoft.AspNetCore.Mvc.Versioning NuGet package.
• Configure API Versioning in Startup.cs (or Program.cs for .NET 6+):

public void ConfigureServices(IServiceCollection services)
{
    services.AddApiVersioning(options =>
    {
        options.ReportApiVersions = true;
        options.AssumeDefaultVersionWhenUnspecified = true;
        options.DefaultApiVersion = new ApiVersion(1, 0);
    });
}

Define Versioned Controllers

[ApiVersion("1.0")]
[Route("api/v{version:apiVersion}/products")]
[ApiController]
public class ProductsV1Controller : ControllerBase
{
    // ... actions for API version 1.0
}

[ApiVersion("2.0")]
[Route("api/v{version:apiVersion}/products")]
[ApiController]
public class ProductsV2Controller : ControllerBase
{
    // ... actions for API version 2.0
}

• Configure Routing: Ensure your routes correctly map to the versioned controllers based on your chosen strategy (e.g., using v{version:apiVersion} in the route template for URL-based versioning).

By implementing API versioning, you can effectively manage the evolution of your RESTful APIs in ASP.NET Core, ensuring a smooth experience for both new and existing clients.

Best Practices

• Deprecate gracefully: Provide clear documentation and sunset timelines.
• Semantic versioning: Use major versions for breaking changes.
• Automated testing: Ensure older versions remain functional.
• Documentation: Maintain version-specific docs for clarity.

Versioning is a strategic decision—URI versioning is often preferred for public APIs due to its simplicity and visibility, while header-based approaches suit internal or hypermedia APIs better.