Top 35 ASP.NET Core Interview Questions and Answers (2026) – Beginner to Advanced

📅 Published: March 2026  |  ⏱ Reading Time: ~18 minutes  |  🏷️ ASP.NET CoreC#Interview.NET 8Web Development

📌 TL;DR: This article covers the 35 most asked ASP.NET Core interview questions for 2026, ranging from beginner concepts like middleware and routing to advanced topics like minimal APIs, gRPC, and performance optimization. Each answer includes code examples and practical explanations. Bookmark this page before your next interview.

📋 Table of Contents

• Introduction
• Section 1 – ASP.NET Core Fundamentals
• Section 2 – Middleware & Request Pipeline 
• Section 3 – Dependency Injection 
• Section 4 – Authentication & Authorization 
• Section 5 – Entity Framework Core 
• Section 6 – Advanced Topics
• Interview Tips
• FAQ
• Key Takeaways

Introduction

ASP.NET Core is one of the most in-demand backend frameworks in 2026, consistently ranking among the top technologies in Stack Overflow Developer Surveys. Whether you are preparing for your first .NET developer role or interviewing for a senior architect position, having a solid grasp of ASP.NET Core concepts is non-negotiable.

This guide covers 35 carefully selected interview questions with detailed answers, real code examples, and difficulty labels so you know exactly what level each question targets. Questions are grouped by topic so you can jump straight to the area you need to review most.

💡 Pro Tip: Interviewers don't just want definitions — they want to see that you understand why something works the way it does. For every answer here, make sure you understand the reasoning, not just the words.

Section 1 – ASP.NET Core Fundamentals

These questions are almost always asked in every .NET interview, regardless of seniority. Master these before anything else.

Q1. What is ASP.NET Core and how is it different from ASP.NET Framework? Beginner

ASP.NET Core is a cross-platform, high-performance, open-source framework for building modern web applications and APIs. It is a complete rewrite of the original ASP.NET Framework, designed from the ground up to run on Windows, Linux, and macOS.

Feature	ASP.NET Framework	ASP.NET Core
Platform	Windows only	Cross-platform
Performance	Moderate	Very high (one of the fastest frameworks)
Hosting	IIS only	IIS, Kestrel, Docker, Nginx
Open Source	Partial	Fully open source
Dependency Injection	Not built-in	Built-in from the start
Latest Version	.NET Framework 4.8 (no new major versions)	.NET 8 / .NET 9 (active development)

Q2. What is the Program.cs file in ASP.NET Core and what is its role? Beginner

Program.cs is the entry point of an ASP.NET Core application. In .NET 6 and later, it uses a minimal hosting model that combines the old Startup.cs and Program.cs into a single file. It is responsible for:

• Creating and configuring the WebApplication builder
• Registering services into the dependency injection container
• Configuring the middleware pipeline
• Running the application

var builder = WebApplication.CreateBuilder(args);

// Register services
builder.Services.AddControllers();
builder.Services.AddDbContext<AppDbContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("Default")));

var app = builder.Build();

// Configure middleware pipeline
app.UseHttpsRedirection();
app.UseAuthentication();
app.UseAuthorization();
app.MapControllers();

app.Run();

Q3. What is Kestrel in ASP.NET Core? Beginner

Kestrel is the default, cross-platform web server built into ASP.NET Core. It is a lightweight, high-performance HTTP server based on libuv (and later on .NET's own async I/O). Kestrel can be used:

• Alone — directly facing the internet in production for simple scenarios
• Behind a reverse proxy — behind Nginx, Apache, or IIS (recommended for production)

Kestrel is what makes ASP.NET Core one of the fastest web frameworks in the world in TechEmpower benchmarks.

Q4. What is the difference between IApplicationBuilder and IServiceCollection? Beginner

These two interfaces serve fundamentally different purposes:

• IServiceCollection — used to register services into the dependency injection container. This happens at application startup before the app runs. Example: builder.Services.AddControllers()
• IApplicationBuilder — used to configure the HTTP request pipeline by adding middleware. Example: app.UseAuthentication()

A simple way to remember: IServiceCollection is about what your app needs, IApplicationBuilder is about how requests are handled.

Q5. What is the difference between AddSingleton, AddScoped, and AddTransient? Beginner

These three methods define the lifetime of a service registered in the DI container:

Lifetime	Created	Shared?	Best For
Singleton	Once per application	Across all requests and users	Configuration, caching, logging
Scoped	Once per HTTP request	Within the same request	Database contexts (EF Core DbContext)
Transient	Every time requested	Never shared	Lightweight, stateless services

builder.Services.AddSingleton<IConfigService, ConfigService>();
builder.Services.AddScoped<IUserRepository, UserRepository>();
builder.Services.AddTransient<IEmailSender, EmailSender>();

⚠️ Common Mistake: Never inject a Scoped service into a Singleton. The Scoped service will behave like a Singleton and can cause data leaks between requests.

Q6. What is Routing in ASP.NET Core? Beginner

Routing is the mechanism that maps incoming HTTP requests to the correct controller action or endpoint. ASP.NET Core supports two main routing approaches:

1. Conventional Routing — defined globally using a URL pattern template:

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

2. Attribute Routing — defined directly on controllers and actions using attributes:

[ApiController]
[Route("api/[controller]")]
public class ProductsController : ControllerBase
{
    [HttpGet("{id}")]
    public IActionResult GetById(int id) { ... }

    [HttpPost]
    public IActionResult Create([FromBody] ProductDto dto) { ... }
}

Attribute routing is preferred for Web APIs because it gives you precise control over URL structure.

Q7. What is the difference between IActionResult and ActionResult<T>? Intermediate

IActionResult is a non-generic interface that can return any HTTP response. ActionResult<T> is a generic version introduced in ASP.NET Core 2.1 that additionally allows returning a strongly-typed object directly, which Swagger/OpenAPI can inspect for documentation.

// IActionResult - no type info for swagger
public IActionResult GetProduct(int id)
{
    var product = _repo.GetById(id);
    if (product == null) return NotFound();
    return Ok(product);
}

// ActionResult<T> - swagger knows the return type is Product
public ActionResult<Product> GetProduct(int id)
{
    var product = _repo.GetById(id);
    if (product == null) return NotFound();
    return product; // implicit conversion to Ok(product)
}

Use ActionResult<T> for API controllers whenever possible.

Q8. What are Model Binding and Model Validation in ASP.NET Core? Beginner

Model Binding automatically maps incoming request data (route values, query strings, form data, JSON body) to action method parameters or model properties.

Model Validation checks that the bound data meets the defined rules using Data Annotation attributes or Fluent Validation.

public class CreateUserDto
{
    [Required]
    [StringLength(100, MinimumLength = 2)]
    public string Name { get; set; }

    [Required]
    [EmailAddress]
    public string Email { get; set; }

    [Range(18, 120)]
    public int Age { get; set; }
}

[HttpPost]
public IActionResult Create([FromBody] CreateUserDto dto)
{
    if (!ModelState.IsValid)
        return BadRequest(ModelState);

    // proceed with valid data
}

When using [ApiController] attribute, model validation errors automatically return a 400 Bad Request — you don't need the ModelState.IsValid check manually.

Q9. What is the [ApiController] attribute and what does it do? Beginner

The [ApiController] attribute enables several API-specific behaviors automatically:

• Automatic model validation — returns 400 if ModelState is invalid
• Binding source inference — complex types are automatically bound from the request body ([FromBody] assumed)
• Problem details responses — error responses follow RFC 7807 format
• Attribute routing requirement — forces use of attribute routing

Q10. What is Configuration in ASP.NET Core and how does it work? Beginner

ASP.NET Core has a flexible configuration system that can read settings from multiple sources in a defined priority order:

1. appsettings.json
2. appsettings.{Environment}.json (e.g. appsettings.Development.json)
3. Environment variables
4. Command line arguments
5. User Secrets (development only)
6. Azure Key Vault (production)

Each source overrides the previous one, so environment variables override appsettings.json.

// appsettings.json
{
  "ConnectionStrings": {
    "Default": "Server=.;Database=MyDb;Trusted_Connection=True"
  },
  "AppSettings": {
    "PageSize": 20
  }
}

// Accessing configuration
var connStr = builder.Configuration.GetConnectionString("Default");
var pageSize = builder.Configuration.GetValue<int>("AppSettings:PageSize");

Q11. What is the Options Pattern in ASP.NET Core? Intermediate

The Options Pattern is a strongly-typed way to bind configuration sections to C# classes, making configuration easier to work with and testable.

// appsettings.json
{
  "EmailSettings": {
    "SmtpHost": "smtp.gmail.com",
    "Port": 587,
    "SenderEmail": "no-reply@triksbuddy.com"
  }
}

// Options class
public class EmailSettings
{
    public string SmtpHost { get; set; }
    public int Port { get; set; }
    public string SenderEmail { get; set; }
}

// Register in Program.cs
builder.Services.Configure<EmailSettings>(
    builder.Configuration.GetSection("EmailSettings"));

// Inject and use
public class EmailService
{
    private readonly EmailSettings _settings;

    public EmailService(IOptions<EmailSettings> options)
    {
        _settings = options.Value;
    }
}

Q12. What is Minimal API in ASP.NET Core? Intermediate

Minimal APIs, introduced in .NET 6, allow building HTTP APIs with minimal code and ceremony — no controllers, no Startup class. They are ideal for microservices and simple APIs.

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();
app.UseSwagger();
app.UseSwaggerUI();

app.MapGet("/products", async (AppDbContext db) =>
    await db.Products.ToListAsync());

app.MapGet("/products/{id}", async (int id, AppDbContext db) =>
    await db.Products.FindAsync(id) is Product p
        ? Results.Ok(p)
        : Results.NotFound());

app.MapPost("/products", async (Product product, AppDbContext db) =>
{
    db.Products.Add(product);
    await db.SaveChangesAsync();
    return Results.Created($"/products/{product.Id}", product);
});

app.Run();

Section 2 – Middleware & Request Pipeline

Middleware is one of the most important ASP.NET Core concepts. Almost every interview will include at least 2-3 questions on this topic.

 

Q13. What is Middleware in ASP.NET Core? Beginner

Middleware is software that is assembled into an application pipeline to handle HTTP requests and responses. Each middleware component can:

• Choose whether to pass the request to the next component
• Perform work before and after the next component in the pipeline

The pipeline is built as a chain of delegates — this is often called the "Russian dolls" model. Common built-in middleware includes: UseHttpsRedirection, UseAuthentication, UseAuthorization, UseStaticFiles, UseRouting.

Q14. How do you create custom middleware in ASP.NET Core? Intermediate

You can create middleware using a class with an InvokeAsync method and a constructor that takes RequestDelegate:

public class RequestLoggingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<RequestLoggingMiddleware> _logger;

    public RequestLoggingMiddleware(RequestDelegate next,
        ILogger<RequestLoggingMiddleware> logger)
    {
        _next = next;
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        _logger.LogInformation(
            "Request: {Method} {Path}",
            context.Request.Method,
            context.Request.Path);

        var stopwatch = Stopwatch.StartNew();
        await _next(context); // call next middleware
        stopwatch.Stop();

        _logger.LogInformation(
            "Response: {StatusCode} in {ElapsedMs}ms",
            context.Response.StatusCode,
            stopwatch.ElapsedMilliseconds);
    }
}

// Register in Program.cs
app.UseMiddleware<RequestLoggingMiddleware>();

Q15. What is the order of middleware execution and why does it matter? Intermediate

Middleware executes in the exact order it is registered in Program.cs. The order matters because each middleware wraps the next one. A request flows in through middleware top-to-bottom, and the response flows out bottom-to-top.

The recommended order for a typical ASP.NET Core app is:

app.UseExceptionHandler();     // 1. Catch all unhandled exceptions
app.UseHsts();                 // 2. HTTP Strict Transport Security
app.UseHttpsRedirection();     // 3. Redirect HTTP to HTTPS
app.UseStaticFiles();          // 4. Serve static files early
app.UseRouting();              // 5. Match routes
app.UseCors();                 // 6. CORS before auth
app.UseAuthentication();       // 7. Who are you?
app.UseAuthorization();        // 8. What can you do?
app.UseResponseCaching();      // 9. Cache after auth
app.MapControllers();          // 10. Execute the endpoint

⚠️ Common Mistake: Putting UseAuthorization() before UseAuthentication() means authorization runs without knowing who the user is. Always authenticate before authorizing.

 

Q16. What is the difference between Use, Run, and Map in middleware? Intermediate

• Use — adds middleware that can call the next middleware in the pipeline
• Run — adds terminal middleware (short-circuits the pipeline, nothing after it runs)
• Map — branches the pipeline based on the request path

app.Use(async (context, next) =>
{
    // runs before next middleware
    await next(context);
    // runs after next middleware
});

app.Map("/health", healthApp =>
{
    healthApp.Run(async context =>
    {
        await context.Response.WriteAsync("Healthy");
    });
});

app.Run(async context =>
{
    await context.Response.WriteAsync("Final middleware - nothing after this runs");
});

Q17. What is Exception Handling Middleware in ASP.NET Core? Intermediate

ASP.NET Core provides several ways to handle exceptions globally:

1. UseExceptionHandler — redirects to an error page or endpoint:

app.UseExceptionHandler("/error");
// or using a lambda:
app.UseExceptionHandler(errorApp =>
{
    errorApp.Run(async context =>
    {
        context.Response.StatusCode = 500;
        context.Response.ContentType = "application/json";
        var error = context.Features.Get<IExceptionHandlerFeature>();
        await context.Response.WriteAsJsonAsync(new {
            message = "An error occurred",
            detail = error?.Error.Message
        });
    });
});

2. Custom Global Exception Middleware — gives you full control over error responses across the entire API.

Q18. What is Response Caching in ASP.NET Core? Intermediate

Response Caching reduces server load by storing HTTP responses and serving them for subsequent identical requests without re-executing the action.

// Register
builder.Services.AddResponseCaching();

// Use in pipeline
app.UseResponseCaching();

// Apply to action
[HttpGet]
[ResponseCache(Duration = 60, Location = ResponseCacheLocation.Any)]
public IActionResult GetProducts()
{
    return Ok(_productService.GetAll());
}

For distributed caching (Redis, SQL Server), use IDistributedCache or libraries like EasyCaching or FusionCache.

Q19. What is CORS and how do you configure it in ASP.NET Core? Beginner

CORS (Cross-Origin Resource Sharing) is a browser security feature that blocks web pages from making requests to a different domain than the one that served the page. ASP.NET Core has built-in CORS support:

// Define a named policy
builder.Services.AddCors(options =>
{
    options.AddPolicy("AllowMyApp", policy =>
    {
        policy.WithOrigins("https://triksbuddy.com", "https://localhost:3000")
              .AllowAnyMethod()
              .AllowAnyHeader()
              .AllowCredentials();
    });
});

// Apply globally
app.UseCors("AllowMyApp");

// Or apply to specific controller/action
[EnableCors("AllowMyApp")]
public class ProductsController : ControllerBase { ... }

Q20. What is Rate Limiting in ASP.NET Core? Advanced

Rate limiting, built into ASP.NET Core 7+, restricts the number of requests a client can make in a given time window — protecting your API from abuse and DDoS attacks.

builder.Services.AddRateLimiter(options =>
{
    options.AddFixedWindowLimiter("fixed", limiterOptions =>
    {
        limiterOptions.PermitLimit = 100;
        limiterOptions.Window = TimeSpan.FromMinutes(1);
        limiterOptions.QueueProcessingOrder = QueueProcessingOrder.OldestFirst;
        limiterOptions.QueueLimit = 10;
    });
    options.RejectionStatusCode = StatusCodes.Status429TooManyRequests;
});

app.UseRateLimiter();

// Apply to endpoint
app.MapGet("/api/data", () => "data").RequireRateLimiting("fixed");

Section 3 – Dependency Injection

Q21. What is Dependency Injection and why is it important? Beginner

Dependency Injection (DI) is a design pattern where an object's dependencies are provided externally rather than created by the object itself. ASP.NET Core has DI built in from the ground up.

Benefits:

• Loose coupling between components
• Easier unit testing (you can inject mocks)
• Better code organization and single responsibility
• Centralized service lifetime management

// Without DI (tightly coupled - bad)
public class OrderService
{
    private readonly EmailService _emailService = new EmailService(); // hard dependency
}

// With DI (loosely coupled - good)
public class OrderService
{
    private readonly IEmailService _emailService;

    public OrderService(IEmailService emailService)
    {
        _emailService = emailService; // injected from outside
    }
}

Q22. What is the difference between constructor injection and property injection? Intermediate

Constructor Injection (preferred in ASP.NET Core) — dependencies are passed through the constructor. The object cannot be created without its dependencies, making them required and explicit.

Property Injection — dependencies are set through public properties after object creation. This makes dependencies optional, which can lead to null reference errors if not carefully managed. ASP.NET Core's built-in DI does not support property injection natively — you need a third-party container like Autofac.

Q23. What is IServiceProvider and when would you use it? Intermediate

IServiceProvider is the interface for the DI container itself. You can use it to resolve services manually (Service Locator pattern) — though this should be avoided in application code as it hides dependencies.

// Avoid this in application code (Service Locator anti-pattern)
public class MyClass
{
    private readonly IServiceProvider _provider;
    public MyClass(IServiceProvider provider) { _provider = provider; }

    public void DoWork()
    {
        var service = _provider.GetRequiredService<IMyService>();
    }
}

// Acceptable use: resolving scoped services from a singleton background service
public class MyBackgroundService : BackgroundService
{
    private readonly IServiceProvider _provider;
    public MyBackgroundService(IServiceProvider provider) { _provider = provider; }

    protected override async Task ExecuteAsync(CancellationToken ct)
    {
        using var scope = _provider.CreateScope();
        var dbContext = scope.ServiceProvider.GetRequiredService<AppDbContext>();
        // use dbContext safely within this scope
    }
}

Q24. What is a Keyed Service in ASP.NET Core 8? Advanced

Keyed Services, introduced in .NET 8, allow registering multiple implementations of the same interface with a unique key, and resolving a specific implementation by key.

// Register multiple implementations with keys
builder.Services.AddKeyedSingleton<IPaymentProcessor, StripeProcessor>("stripe");
builder.Services.AddKeyedSingleton<IPaymentProcessor, PayPalProcessor>("paypal");

// Resolve by key
public class CheckoutService
{
    private readonly IPaymentProcessor _processor;

    public CheckoutService([FromKeyedServices("stripe")] IPaymentProcessor processor)
    {
        _processor = processor;
    }
}

Section 4 – Authentication & Authorization

Q25. What is the difference between Authentication and Authorization? Beginner

• Authentication — verifies who you are (identity). "Are you really John?"
• Authorization — verifies what you can do (permissions). "Can John access this admin page?"

In ASP.NET Core, UseAuthentication() must always come before UseAuthorization() in the pipeline.

Q26. What is JWT and how is it used in ASP.NET Core? Intermediate

JWT (JSON Web Token) is a compact, self-contained token format used for stateless authentication. A JWT contains three Base64-encoded parts: Header, Payload (claims), and Signature.

// Configure JWT Authentication
builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(options =>
    {
        options.TokenValidationParameters = new TokenValidationParameters
        {
            ValidateIssuer = true,
            ValidateAudience = true,
            ValidateLifetime = true,
            ValidateIssuerSigningKey = true,
            ValidIssuer = builder.Configuration["Jwt:Issuer"],
            ValidAudience = builder.Configuration["Jwt:Audience"],
            IssuerSigningKey = new SymmetricSecurityKey(
                Encoding.UTF8.GetBytes(builder.Configuration["Jwt:Key"]))
        };
    });

// Generate a token
var claims = new[]
{
    new Claim(ClaimTypes.Name, user.Username),
    new Claim(ClaimTypes.Role, user.Role)
};

var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_config["Jwt:Key"]));
var token = new JwtSecurityToken(
    issuer: _config["Jwt:Issuer"],
    audience: _config["Jwt:Audience"],
    claims: claims,
    expires: DateTime.UtcNow.AddHours(1),
    signingCredentials: new SigningCredentials(key, SecurityAlgorithms.HmacSha256)
);

Q27. What is Policy-Based Authorization in ASP.NET Core? Intermediate

Policy-based authorization provides more flexibility than simple role checks. You define named policies with requirements, then apply them to controllers or actions.

// Define policies
builder.Services.AddAuthorization(options =>
{
    options.AddPolicy("AdminOnly", policy =>
        policy.RequireRole("Admin"));

    options.AddPolicy("MinimumAge", policy =>
        policy.Requirements.Add(new MinimumAgeRequirement(18)));

    options.AddPolicy("PremiumUser", policy =>
        policy.RequireClaim("subscription", "premium"));
});

// Apply to controller
[Authorize(Policy = "AdminOnly")]
public class AdminController : ControllerBase { ... }

[Authorize(Policy = "MinimumAge")]
public IActionResult GetAdultContent() { ... }

 

Section 5 – Entity Framework Core

Q28. What is Entity Framework Core? Beginner

Entity Framework Core (EF Core) is the official ORM (Object-Relational Mapper) for .NET. It lets you work with a database using .NET objects, eliminating most of the data-access code you would otherwise write. EF Core supports SQL Server, MySQL, PostgreSQL, SQLite, and more.

EF Core supports three development approaches:

• Code First — define your model in C# classes, EF generates the database
• Database First — scaffold C# models from an existing database
• Model First — less common, design through a visual designer

Q29. What is the difference between DbContext and DbSet<T>? Beginner

• DbContext — represents a session with the database. It manages connections, change tracking, and saving data. You inherit from it to create your application context.
• DbSet<T> — represents a table in the database. Each DbSet property on your DbContext corresponds to a database table.

public class AppDbContext : DbContext
{
    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) { }

    public DbSet<Product> Products { get; set; }
    public DbSet<Category> Categories { get; set; }
    public DbSet<Order> Orders { get; set; }
}

Q30. What is Lazy Loading vs Eager Loading vs Explicit Loading in EF Core? Intermediate

Strategy	When Data is Loaded	How
Eager Loading	With the main query	.Include()
Lazy Loading	When navigation property is accessed	Proxy or UseLazyLoadingProxies()
Explicit Loading	Manually triggered after initial load	.Entry().Collection().LoadAsync()

// Eager Loading (recommended for most cases)
var orders = await db.Orders
    .Include(o => o.Customer)
    .Include(o => o.Items)
        .ThenInclude(i => i.Product)
    .ToListAsync();

// Explicit Loading
var order = await db.Orders.FindAsync(1);
await db.Entry(order).Collection(o => o.Items).LoadAsync();

⚠️ N+1 Problem: Lazy Loading can cause the N+1 query problem — 1 query for the list, then N queries for each related entity. Prefer Eager Loading in performance-sensitive code.

 

Section 6 – Advanced Topics

Q31. What is gRPC in ASP.NET Core and when would you use it? Advanced

gRPC is a high-performance, open-source RPC (Remote Procedure Call) framework that uses HTTP/2 and Protocol Buffers (protobuf) for serialization. It is significantly faster than REST for inter-service communication in microservices.

Use gRPC when:

• Building microservices that communicate internally
• You need real-time bidirectional streaming
• Performance and bandwidth efficiency are critical

Use REST when:

• Building public APIs consumed by browsers or third parties
• You need broad compatibility without special client libraries

Q32. What is SignalR and what is it used for? Intermediate

SignalR is an ASP.NET Core library that enables real-time, bidirectional communication between server and clients. It automatically chooses the best transport (WebSockets, Server-Sent Events, or Long Polling) based on what the client supports.

Common use cases: chat applications, live notifications, real-time dashboards, collaborative editing, live sports scores.

// Hub definition
public class NotificationHub : Hub
{
    public async Task SendNotification(string userId, string message)
    {
        await Clients.User(userId).SendAsync("ReceiveNotification", message);
    }
}

// Register
builder.Services.AddSignalR();
app.MapHub<NotificationHub>("/notifications");

Q33. What are Background Services in ASP.NET Core? Intermediate

Background Services are long-running tasks that run in the background of your ASP.NET Core application. You implement IHostedService or extend BackgroundService.

public class EmailQueueProcessor : BackgroundService
{
    private readonly ILogger<EmailQueueProcessor> _logger;

    public EmailQueueProcessor(ILogger<EmailQueueProcessor> logger)
    {
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            _logger.LogInformation("Processing email queue...");
            // do work here
            await Task.Delay(TimeSpan.FromSeconds(30), stoppingToken);
        }
    }
}

// Register
builder.Services.AddHostedService<EmailQueueProcessor>();

Q34. What is Health Checks in ASP.NET Core? Intermediate

Health Checks provide an endpoint that reports the health status of your application and its dependencies (database, external APIs, etc.). They are essential for container orchestration systems like Kubernetes.

builder.Services.AddHealthChecks()
    .AddSqlServer(connectionString: builder.Configuration.GetConnectionString("Default"))
    .AddUrlGroup(new Uri("https://api.thirdparty.com/health"), name: "third-party-api")
    .AddCheck<CustomHealthCheck>("custom");

app.MapHealthChecks("/health", new HealthCheckOptions
{
    ResponseWriter = UIResponseWriter.WriteHealthCheckUIResponse
});

Q35. How do you optimize performance in ASP.NET Core APIs? Advanced

Performance optimization in ASP.NET Core covers multiple layers:

• Use async/await everywhere — never block threads with .Result or .Wait()
• Response compression — enable Brotli/GZip compression
• Output caching — use AddOutputCache() in .NET 7+
• EF Core optimization — use AsNoTracking() for read-only queries, select only needed columns with Select()
• Use IAsyncEnumerable — stream large result sets instead of loading all into memory
• Connection pooling — EF Core and ADO.NET handle this automatically with properly configured connection strings
• Avoid N+1 queries — use eager loading or projections
• Use Span<T> and Memory<T> for high-performance string and buffer processing

// Read-only query optimization
var products = await db.Products
    .AsNoTracking()
    .Where(p => p.IsActive)
    .Select(p => new ProductDto { Id = p.Id, Name = p.Name })
    .ToListAsync();

💼 Interview Tips for ASP.NET Core Roles

• Know the pipeline order cold. Drawing the middleware pipeline on a whiteboard is a very common interview exercise.
• Understand DI lifetimes deeply. Scoped vs Singleton mistakes are a common source of bugs — interviewers love this topic.
• Be ready for "how would you secure your API?" — cover JWT, HTTPS, rate limiting, input validation, and CORS.
• Know at least one real performance optimization you've done or studied — AsNoTracking, caching, async queries.
• Mention .NET 8 features if possible — Keyed Services, Native AOT, Frozen Collections — these signal you stay current.

❓ Frequently Asked Questions

What .NET version should I study for interviews in 2026?

Focus on .NET 8 (LTS) as your primary reference. Most companies that are actively hiring are on .NET 6, 7, or 8. Understanding the concepts matters more than version-specific syntax, but being aware of .NET 8 features signals that you stay current.

Is knowing Entity Framework Core enough for database questions?

EF Core covers most interview questions, but also be familiar with raw ADO.NET and Dapper (a lightweight ORM). Senior roles may ask when you'd choose Dapper over EF Core — the answer is performance-critical, high-volume read scenarios.

Do I need to know Blazor for ASP.NET Core interviews?

Only if the job description mentions it. For backend/API roles, Blazor knowledge is a bonus, not a requirement. For full-stack .NET roles, knowing Blazor Server vs Blazor WebAssembly is increasingly valuable.

What is the difference between REST and gRPC — when is each asked?

This question appears in senior and microservices-focused interviews. REST is for external APIs, gRPC is for internal service-to-service communication where performance is critical.

✅ Key Takeaways

• ASP.NET Core is cross-platform, high-performance, and fully open source — fundamentally different from the old ASP.NET Framework
• The middleware pipeline order matters — always authenticate before authorizing
• DI service lifetimes (Singleton, Scoped, Transient) are one of the most tested topics — know them deeply
• JWT is the standard for stateless API authentication — understand how to generate and validate tokens
• EF Core's AsNoTracking() and eager loading are key performance tools
• Minimal APIs, Keyed Services, and Rate Limiting are .NET 6-8 features worth knowing for modern interviews

---

Found this helpful? Share it with a friend preparing for their .NET interview. Drop your questions in the comments below — we read and reply to every one.