Senior ASP.NET Web API Interview Questions

Common Web API design patterns improve maintainability, scalability, and testability:

• Repository Pattern – Abstracts data access; simplifies unit testing and business logic separation.
• Unit of Work – Groups operations under a single transaction for consistency.
• CQRS – Separates read and write operations for scalability and performance.
• Mediator / MediatR – Decouples request-handling logic using command/query handlers.
• Decorator Pattern – Adds logging, caching, or auditing without modifying core business logic.

Centralized logging ensures consistent tracking across all API requests.

• Use ILogger<T> via dependency injection.
• Capture structured logs with levels (Trace ? Critical).
• Write logs to console, files, databases, or providers like Seq, ELK, Splunk, or Application Insights.
• Use middleware to log incoming requests, outgoing responses, and execution duration.

To log request/response bodies safely:

• Use custom middleware to intercept HTTP pipeline.
• Enable request buffering using HttpRequest.EnableBuffering().
• Buffer and copy response streams using a wrapper.
• Avoid logging sensitive fields such as passwords, tokens, and PII.
• Include traceId or correlationId for cross-service tracking.

Effective caching improves performance and reduces database load:

• Use the [ResponseCache] attribute for client caching.
• Use server-side caching middleware for heavy endpoints.
• Leverage distributed caches like Redis or Memcached for load-balanced apps.
• Apply cache invalidation strategies to prevent stale data.

Swagger/OpenAPI improves discoverability and client integration.

• Install Swashbuckle.AspNetCore.
• Configure AddSwaggerGen() in Program.cs.
• Include XML comments for controllers and models.
• Support authentication, versioning, schema examples, and UI customization.

Large-scale APIs require structured endpoint organization:

• Use feature-based folder structure instead of traditional controller-based.
• Group routes using /api/v1/[module]/[controller].
• Use Areas for large domains.
• Apply consistent naming and versioning strategies.

To handle async exceptions:

• Wrap async operations in try/catch.
• Ensure thrown exceptions bubble to global exception middleware.
• Capture structured logs for debugging.
• Avoid async void except for event handlers.

Health checks monitor service and dependency availability.

• Use Microsoft.Extensions.Diagnostics.HealthChecks.
• Expose a /health endpoint.
• Check database connections, external APIs, disk, cache, etc.
• Integrate with monitoring tools (Kubernetes, Azure, AWS, Prometheus).