10 minlesson

API Production Readiness

API Production Readiness

You have built a fully functional parcel tracking API with domain models, business rules, search, analytics, and error handling. Before shipping it to real consumers, you need to address the concerns that separate a working prototype from a production-grade service.

What Production Readiness Means

A production-ready API is one that external developers can discover, understand, integrate with, and depend on. It goes beyond correct request handling to include:

  • Discoverability -- Consumers need documentation to learn what endpoints exist and how to call them.
  • Stability -- Versioning lets you evolve the API without breaking existing integrations.
  • Observability -- Health checks and structured logging give operations teams confidence that the service is running correctly.
  • Security boundaries -- CORS and rate limiting protect the API from abuse and control which origins can call it.

Each of these concerns maps to a specific middleware or library that ASP.NET Core provides out of the box or through a well-supported NuGet package.

OpenAPI Documentation

OpenAPI (formerly Swagger) is the industry standard for describing REST APIs. ASP.NET Core 10 includes built-in OpenAPI document generation through Microsoft.AspNetCore.OpenApi.

A good OpenAPI setup includes:

  • Endpoint descriptions pulled from XML documentation comments on your controller actions.
  • Request and response examples so consumers see the expected shape of payloads.
  • Grouping by feature area using tags, so related endpoints appear together.
  • Schema descriptions for your DTOs so each property is explained.

Swagger UI or Scalar then renders the OpenAPI document as an interactive page where developers can try out endpoints directly.

API Versioning

APIs change over time. When you add a new required field or restructure a response, existing clients may break. API versioning solves this by letting multiple versions coexist:

  • URL-based versioning (/api/v1/parcels) is the most visible and cache-friendly strategy.
  • Header-based versioning uses a custom header like X-Api-Version.
  • Query string versioning uses ?api-version=1.0.

The Asp.Versioning.Mvc package provides clean versioning support for ASP.NET Core. URL-based versioning is the approach most widely adopted by public APIs (Stripe, GitHub, Twilio) because it is explicit and easy to reason about.

Health Checks

A health check endpoint answers the question: "Is this service working right now?" Orchestrators like Kubernetes, load balancers, and monitoring dashboards poll health endpoints to decide whether to route traffic to an instance.

ASP.NET Core has a built-in health check framework:

csharp
1builder.Services.AddHealthChecks()
2    .AddCheck("database", () =>
3    {
4        // verify database connectivity
5        return HealthCheckResult.Healthy();
6    });
7

8app.MapHealthChecks("/health");

A minimal health check verifies database connectivity. More advanced setups check external dependencies like message queues, caches, or third-party APIs.

Liveness vs. Readiness

  • Liveness -- The process is running and not deadlocked. If liveness fails, the orchestrator restarts the container.
  • Readiness -- The service can accept traffic. If readiness fails, the load balancer stops sending requests until it recovers.

You can expose separate endpoints (/health/live and /health/ready) with different check sets.

CORS (Cross-Origin Resource Sharing)

Browsers enforce the same-origin policy: JavaScript on https://frontend.example.com cannot call https://api.example.com unless the API explicitly allows it through CORS headers.

CORS configuration in ASP.NET Core specifies:

  • Allowed origins -- Which domains can call the API.
  • Allowed methods -- Which HTTP methods (GET, POST, PUT, DELETE) are permitted.
  • Allowed headers -- Which request headers the client can send.
  • Exposed headers -- Which response headers the client can read.

For a parcel tracking API consumed by a frontend application, you would allow the frontend origin and the standard methods your API uses.

Rate Limiting

Rate limiting protects your API from being overwhelmed by too many requests. Without it, a single misbehaving client can degrade the service for everyone.

ASP.NET Core 7+ includes Microsoft.AspNetCore.RateLimiting middleware with built-in algorithms:

  • Fixed window -- A counter resets at regular intervals (e.g., 100 requests per minute).
  • Sliding window -- Smooths out bursts by dividing the window into segments.
  • Token bucket -- Allows short bursts while enforcing an average rate.
  • Concurrency limiter -- Limits how many requests run at the same time.

For a parcel tracking API, a fixed window limiter of 100 requests per minute per client IP is a reasonable starting point. Clients that exceed the limit receive a 429 Too Many Requests response.

Request/Response Logging

Structured logging of HTTP requests and responses provides an audit trail and helps diagnose issues. Key data points to log include:

  • Request method, path, and query string
  • Response status code and elapsed time
  • Correlation IDs for tracing requests across services

ASP.NET Core provides UseHttpLogging middleware and you can write custom middleware for more control over what gets logged. Avoid logging sensitive data like authorization headers or request bodies containing passwords.

Correlation IDs

A correlation ID is a unique identifier assigned to each incoming request. It flows through every log entry produced during that request, making it possible to trace a single user action across multiple log lines.

For APIs that call other downstream services, propagating the correlation ID in outgoing requests lets you trace a single operation across the entire system. This is essential for debugging in distributed architectures.

Environment-Specific Configuration

Production readiness is not just about adding middleware. It also means configuring the application differently based on the environment:

  • Development -- Enable Swagger UI, use permissive CORS, show detailed error messages.
  • Staging -- Mirror production configuration but point to test databases.
  • Production -- Restrict CORS origins, hide Swagger UI, use structured JSON logging, enable rate limiting.

ASP.NET Core makes this straightforward with appsettings.{Environment}.json files and the IsDevelopment() / IsProduction() checks in Program.cs. Feature flags and environment variables give you additional control without redeploying code.

Putting It All Together

In a typical Program.cs, the production-readiness middleware is registered in this order:

csharp
1// Services
2builder.Services.AddOpenApi();
3builder.Services.AddApiVersioning();
4builder.Services.AddHealthChecks();
5builder.Services.AddCors();
6builder.Services.AddRateLimiter();
7

8// Middleware pipeline
9app.UseHttpLogging();
10app.UseCors();
11app.UseRateLimiter();
12app.UseAuthentication();
13app.UseAuthorization();
14

15app.MapHealthChecks("/health");
16app.MapControllers();

The order matters. CORS must run before routing returns responses. Rate limiting should run early to reject excess requests before they consume resources.

Summary

In this lesson, you learned the key concerns for making an API production-ready:

  • OpenAPI documentation makes your API discoverable and self-describing
  • API versioning lets you evolve endpoints without breaking existing clients
  • Health checks give orchestrators and monitoring tools a way to verify service status
  • CORS controls which browser-based clients can call your API
  • Rate limiting protects against request floods and ensures fair usage
  • Structured logging provides an audit trail for debugging and monitoring

In the following presentations, you will configure each of these features in detail for the parcel tracking API.

API Production Readiness - Anko Academy