Interview Q&A

Answer: sync filters implement IAsyncActionFilter and support await, improving scalability.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

🏦 Fintech API – Global Exception Filter

Ensures consistent error envelopes across microservices.

🛠 Microservices – Audit Logging

Tracks when sensitive controller actions are executed.

👮 Role-based Authorization

Custom authorization filter validating role claims dynamically.

🚀 Performance Profiling

Times how long each controller method takes.

public class ProfilingFilter : IActionFilter
{
private Stopwatch _watch;
public void OnActionExecuting(ActionExecutingContext context)
{
_watch = Stopwatch.StartNew();
}
public void OnActionExecuted(ActionExecutedContext context)
{

_watch.Stop();

Console.WriteLine($"Action took {_watch.ElapsedMilliseconds}

ms");

}
}

custom page or handler.

Example:

if (env.IsDevelopment())

pp.UseDeveloperExceptionPage();

else

pp.UseExceptionHandler("/Error");

Or inline:

pp.UseExceptionHandler(errorApp =>

{

errorApp.Run(async context =>

{
context.Response.StatusCode = 500;

wait context.Response.WriteAsync("An error

occurred");

});

});

(UseExceptionHandler, UseDeveloperExceptionPage)

• UseDeveloperExceptionPage() shows detailed errors (development

only).

• UseExceptionHandler("/Error") handles errors in production with

a custom page or handler.

Example:

if (env.IsDevelopment())

app.UseDeveloperExceptionPage();

else

app.UseExceptionHandler("/Error");

Or inline:

app.UseExceptionHandler(errorApp =>

errorApp.Run(async context =>

context.Response.StatusCode = 500;

await context.Response.WriteAsync("An error

occurred");

});

});

Yes. They form a pipeline based on their defined order.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Filters execute per controller action → use sparingly. Avoid heavy DB calls. Avoid creating new HttpClients or DbContexts inside filters. Prefer asynchronous filters.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: pp.UseHttpsRedirection(); dd early in the pipeline, before auth or routing. You can configure HTTPS ports in launchSettings.json or ppsettings.json.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Redirects HTTP requests to HTTPS. app.UseHttpsRedirection(); Add early in the pipeline, before auth or routing. You can configure HTTPS ports in launchSettings.json or appsettings.json.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Use:

• ActionExecutingContext mocks
• ActionExecutedContext mocks
• DefaultHttpContext

var httpContext = new DefaultHttpContext();
var context = new ActionExecutingContext(...);

Focus tests on:

• Expected results
• Short-circuiting behavior
• Context manipulation

pp.UseStaticFiles(new StaticFileOptions

{

FileProvider = new

PhysicalFileProvider(Path.Combine(env.ContentRootPath,

"MyFiles")),

RequestPath = "/Files",

OnPrepareResponse = ctx =>

{

ctx.Context.Response.Headers.Append("Cache-Control",

"public,max-age=600");
}

});

For directory browsing:

pp.UseDirectoryBrowser(new DirectoryBrowserOptions

{

FileProvider = new PhysicalFileProvider("path"),

RequestPath = "/browse"

});

Mistake Fix

Doing authentication inside action filters Use authorization filters

Performing heavy logic Move to middleware

Not registering filters as services Use DI for maintainability

Returning inconsistent error messages Handle errors via global exception filter

Answer: pp.Run(async ctx => { wait ctx.Response.WriteAsync("This ends the pipeline"); });

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

middleware

Type Description

Terminal Ends the pipeline. Doesn’t call next(). E.g., app.Run()

Non-Termi

nal

Calls next() and allows other middlewares to run after it.

E.g., app.Use()

Terminal middleware:

app.Run(async ctx => {

await ctx.Response.WriteAsync("This ends the pipeline");

});

Yes—action filters have full access to ActionArguments.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

pp.UseAuthentication(); // Validates user identity

pp.UseAuthorization(); // Applies policies/roles

Order matters: must be after routing but before endpoints.

pp.UseRouting();

pp.UseAuthentication();

pp.UseAuthorization();

pp.UseEndpoints(...);

• Filters provide clean, reusable cross-cutting logic for MVC pipelines.
• Use the right filter type for the right stage.
• Prefer middleware when you don’t need controller context.
• Exception filters are best for consistent error handling.
• Use DI for scalable, clean, testable filter implementations.
• Filters shine in enterprise applications: auditing, authorization, and response shaping.

Answer: Exception filters only catch exceptions from MVC actions; middleware catches exceptions from the entire pipeline.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

pp.UseCors("MyPolicy"); Must be placed before routing/endpoints.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: builder.Services.AddCors(options => options.AddPolicy("MyPolicy", policy => policy.WithOrigins(" .AllowAnyHeader() .AllowAnyMethod(); }); }); app.UseCors("MyPolicy"); Must be placed before routing/endpoints.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: wait _next(context); sw.Stop(); Console.WriteLine($"Request took {sw.ElapsedMilliseconds} ms"); } } Register: pp.UseMiddleware<TimingMiddleware>(); Dependency Injection (DI)

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

execution time)

Example custom middleware to measure time:

public class TimingMiddleware

private readonly RequestDelegate _next;

public TimingMiddleware(RequestDelegate next) => _next =

next;

public async Task InvokeAsync(HttpContext context)

var sw = Stopwatch.StartNew();

await _next(context);

sw.Stop();

Console.WriteLine($"Request took

{sw.ElapsedMilliseconds} ms");

Register:

app.UseMiddleware<TimingMiddleware>();

Dependency Injection (DI)

Filters specifically built for Minimal APIs (introduced in ASP.NET Core 7).

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

✅ Capabilities:

• Constructor injection
• Lifetime management (Transient, Scoped, Singleton)
• Supports IEnumerable<T>, IServiceProvider, and open generics

⚠ Limitations:

• No support for named registrations
• Limited property injection
• Basic feature set compared to Autofac or other 3rd-party containers

Answer: Lifetime Description Use Case Example Transient New instance every time Lightweight stateless services Scoped One instance per request Database context, UoW Singleto One instance for the app's lifetime Logging, Config access

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Lower order executes first on entry but last on exit—like nested layers.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.