.NET Core Interview Questions and Answers for 10+ Years Experienced Professionals

 

🔹 Core Concepts

Q1. What are the key differences between .NET Framework, .NET Core, and .NET 5/6/7+?
Answer:

• .NET Framework – Windows-only, older, supports legacy apps.

• .NET Core – Cross-platform (Windows, Linux, macOS), modular, open-source, better performance.

• .NET 5+ (unified platform) – Combines .NET Core and .NET Framework into one platform with continuous updates (no ".NET Core 4").

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Q2. Explain the Middleware pipeline in ASP.NET Core.
Answer:

• Middleware is a software component that processes HTTP requests and responses.

• It forms a pipeline where each component can handle, pass, or short-circuit a request.

• Example:

  app.UseRouting();
  app.UseAuthentication();
  app.UseAuthorization();
  app.UseEndpoints(endpoints => { endpoints.MapControllers(); });
  

• Custom middleware can be added using app.Use(...).

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Q3. What are Hosting Models in .NET Core?
Answer:

• In-Process hosting – App runs inside IIS worker process (w3wp.exe), better performance.

• Out-of-Process hosting – App runs as a separate process (dotnet.exe) with IIS as a reverse proxy.

• Self-hosted (Kestrel only) – Runs without IIS, often used in Docker or Linux environments.

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🔹 Advanced & Architecture

Q4. How do you implement Dependency Injection (DI) in .NET Core?
Answer:

• Built-in DI container (IServiceCollection).

• Register services:

  services.AddTransient<IService, Service>();
  services.AddScoped<IService, Service>();
  services.AddSingleton<IService, Service>();
  

• Lifetime depends on usage:

  • Transient – new instance every time.

  • Scoped – one per request.

  • Singleton – one per application lifetime.

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Q5. How do you handle Configuration in .NET Core?
Answer:

• Configuration is hierarchical and supports multiple providers: JSON, environment variables, secrets, Azure Key Vault.

• Example:

  var builder = WebApplication.CreateBuilder(args);
  var myValue = builder.Configuration["MySettings:Key"];
  

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Q6. Explain the difference between IHostedService and BackgroundService.
Answer:

• IHostedService – Base contract for long-running tasks.

• BackgroundService – Abstract class simplifying background task creation by overriding ExecuteAsync.

• Example use cases: background jobs, message queue processing, cleanup tasks.

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🔹 Performance & Optimization

Q7. How do you improve performance in .NET Core applications?
Answer:

• Use AsNoTracking in EF Core for read-only queries.

• Implement caching (in-memory, distributed like Redis).

• Optimize database calls (batch queries, stored procedures).

• Enable response compression and HTTP/2.

• Use ValueTask instead of Task when suitable.

• Minimize memory allocations (e.g., Span<T>, Memory<T>).

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Q8. What is the difference between Task, ValueTask, and IAsyncEnumerable?
Answer:

• Task – standard async operation, always allocates.

• ValueTask – avoids allocation if operation is already completed. Useful in high-performance scenarios.

• IAsyncEnumerable<T> – asynchronous streaming, allows processing items as they arrive instead of waiting for the full collection.

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🔹 Security & Best Practices

Q9. How do you secure an ASP.NET Core API?
Answer:

• Use JWT (JSON Web Tokens) for stateless authentication.

• Implement Role-Based and Policy-Based authorization.

• Secure secrets with Azure Key Vault or User Secrets.

• Enable HTTPS redirection, CORS policies, and Data Protection APIs.

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Q10. Explain Data Protection in .NET Core.
Answer:

• Protects sensitive data like cookies, tokens, and CSRF.

• Provides APIs for encryption and decryption with key rotation.

• Keys are stored locally or in Azure Key Vault/Redis for distributed systems.

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🔹 Cloud & Microservices

Q11. How do you deploy .NET Core apps in Docker and Kubernetes?
Answer:

• Create a Dockerfile:

  FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS base
  WORKDIR /app
  COPY . .
  ENTRYPOINT ["dotnet", "MyApp.dll"]
  

• Push image to Azure Container Registry / DockerHub.

• Deploy using Kubernetes Deployment + Service + Ingress.

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Q12. What patterns do you use in microservices with .NET Core?
Answer:

• API Gateway (e.g., Ocelot).

• Circuit Breaker (Polly).

• Event-driven architecture with Kafka/RabbitMQ.

• CQRS + Event Sourcing for complex domains.

• Distributed caching for scalability.

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🔹 Entity Framework Core

Q13. Difference between EF Core and Dapper?
Answer:

• EF Core – Full ORM, LINQ, migrations, change tracking, slower but easier.

• Dapper – Micro ORM, lightweight, faster for raw SQL queries, no change tracking.

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Q14. How do you handle migrations in EF Core in production?
Answer:

• Maintain migrations in version control.

• Use dotnet ef migrations add and dotnet ef database update.

• In CI/CD, run migrations automatically or via tools like Flyway/Liquibase for safe rollbacks.

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🔹 System Design & Scaling

Q15. How would you design a high-traffic .NET Core API?
Answer:

• Use Load Balancers + horizontal scaling.

• Cache frequently accessed data (Redis/Memory).

• Optimize database with read replicas.

• Use CQRS to separate read/write workloads.

• Implement async communication with queues.

• Deploy with Kubernetes + autoscaling.