Sunday, November 23, 2025

⭐ Top 50 .NET Interview Questions and Answers (Fully Explained) (Perfect for Freshers + Experienced .NET Developers)-2025

1. What is .NET Framework?

Answer:
.NET Framework is a Microsoft software development platform used to build Windows, Web, and Enterprise applications. It includes:

CLR (Common Language Runtime)
BCL (Base Class Library)
Languages: C#, VB.NET, F#
Tools: Visual Studio

It allows cross-language interoperability and simplifies memory management via the CLR.

2. What is .NET Core / .NET 5+?

Answer:
.NET Core (now unified under .NET 5, .NET 6, .NET 7, .NET 8) is:

Cross-platform (Windows, Linux, macOS)
Open-source
High-performance and lightweight
Supports microservices, containers, and cloud-native apps

It replaced the old .NET Framework with a unified modern platform.

3. What is the CLR?

Answer:
CLR (Common Language Runtime) is the runtime environment of .NET.
It handles:

Memory management
Garbage Collection
Thread management
Exception handling
Code execution
Security

It converts MSIL (Microsoft Intermediate Language) into native machine code.

4. What is the difference between .NET Framework and .NET Core?

Answer:

Feature	.NET Framework	.NET Core/.NET 6+
Platform	Windows-only	Cross-platform
Open Source	Limited	Fully open-source
Performance	Moderate	High-performance
Deployment	System-level	Side-by-side
Architecture	Monolithic	Modular

.NET Core is recommended for modern applications, cloud applications, and microservices.

5. What is C#?

Answer:
C# (C Sharp) is an object-oriented programming language developed by Microsoft.
Features:

Strongly typed
OOP-based
Garbage-collected
Supports LINQ, async/await, generics
Used for web, desktop, API, game development (Unity), cloud apps.

6. What is MSIL/IL Code?

Answer:
MSIL (or IL) is the intermediate code generated after compiling C# code.
CLR converts IL to native code using JIT (Just-In-Time) compiler.

7. What is JIT Compiler?

Answer:
JIT Compiler converts MSIL into machine code during program execution.
Types of JIT:

Pre-JIT
Econo-JIT
Normal JIT

This improves performance and optimizes based on runtime.

8. What is OOPS in C#?

Answer:
OOPS stands for:

Encapsulation
Abstraction
Inheritance
Polymorphism

It helps create modular, maintainable, and reusable code.

9. Explain Encapsulation with example.

Answer:
Encapsulation hides internal object details and exposes only required functionality.

Example:


public class BankAccount 
{
    private decimal balance;

    public void Deposit(decimal amount) => balance += amount;

    public decimal GetBalance() => balance;
}

Here, balance is protected from direct access.

10. What is Inheritance in C#?

Answer:
Inheritance allows one class to inherit properties and methods of another.

Example:


class Car { public void Drive() {} }
class BMW : Car { }

BMW inherits Drive().

11. What is Polymorphism?

Answer:
Polymorphism allows methods to behave differently based on runtime objects.

Example:


public virtual void Message() { }
public override void Message() { }

12. Difference between Abstract Class and Interface.

Answer:

Abstract Class	Interface
Can have fields	No fields
Can have constructors	No constructors
Supports abstract + concrete methods	Only abstract methods
Single inheritance only	Multiple inheritance

13. What are Value Types and Reference Types?

Answer:

Value types: stored in stack → int, double, struct
Reference types: stored in heap → class, array, string

14. What is Boxing and Unboxing?

Answer:
Boxing: Converting value type → object (heap)
Unboxing: Converting object → value type

Example:


int x = 10;
object obj = x; // Boxing
int y = (int)obj; // Unboxing

15. What is ASP.NET Core?

Answer:
A high-performance, cross-platform framework for building:

Web apps
REST APIs
Microservices
Cloud applications

Uses Middleware and Dependency Injection by default.

16. What are Middleware components?

Answer:
Middleware is a pipeline that handles HTTP requests in sequence.
Examples:

Authentication
Routing
Exception handling
Logging

Implemented like:


app.UseMiddleware<CustomMiddleware>();

17. What is Dependency Injection (DI)?

Answer:
A design pattern where dependencies are injected instead of being created inside classes.

Example:


services.AddScoped<IEmployeeService, EmployeeService>();

Benefits:

Testability
Loose coupling
Readability

18. What is Entity Framework Core?

Answer:
EF Core is an ORM (Object Relational Mapper) for .NET used to interact with databases using C# instead of SQL.

Features:

Migrations
LINQ queries
Change tracking
Database-first & Code-first support

19. What is Code-First approach?

You create C# classes → EF creates database tables automatically.

20. What is Database-First approach?

Database already exists → EF generates models and DbContext.

21. What is Migration in EF Core?

Answer:
Migrations track database schema changes.

Commands:


Add-Migration Init
Update-Database

22. What is LINQ?

Answer:
Language Integrated Query to perform queries on objects, collections, datasets, and DB.

Example:


var data = list.Where(x => x.Age > 20);

23. What is async and await?

Answer:
Used for asynchronous programming to avoid thread blocking.

Example:


await Task.Delay(1000);

24. What is Garbage Collection in .NET?

Answer:
Automatic memory management that frees unused objects.

Generations:

Gen 0
Gen 1
Gen 2

25. What is IDisposable Interface?

Used to release unmanaged resources manually.

Example:


using(var conn = new SqlConnection()) { }

26. What is a Constructor and Destructor?

Constructor → initializes object
Destructor → frees resources (rare in .NET)

27. What is Singleton Pattern?

Ensures only one instance of a class exists.

Example:


public static readonly Singleton Instance = new Singleton();

28. What is Routing in ASP.NET Core?

Matches incoming HTTP requests to endpoints.

Example:


app.MapControllerRoute("default", "{controller}/{action}/{id?}");

29. What is Model Binding?

ASP.NET Core automatically maps request data to parameters or models.

30. What is ViewModel?

A DTO used between View and Controller to avoid exposing domain models.

31. What is REST API?

Architectural style for building stateless, resource-based web services.

32. Difference between GET and POST.

GET → Fetch data (idempotent)
POST → Create data (not idempotent)

33. What is JWT Token?

A secure token used for authentication between client and server.
Parts:

Header
Payload
Signature

34. What is Swagger?

API documentation and testing tool built on OpenAPI specification.

35. What is Microservices Architecture?

Application broken into independent services.
Benefits: scalability, fault isolation, cloud readiness.

36. What is Kestrel?

The built-in high-performance web server in ASP.NET Core.

37. What is Configuration in ASP.NET Core?

Manages app settings using:

appsettings.json
Environment variables
Azure Key Vault

38. What is CORS?

Cross-Origin Resource Sharing → Allows frontend apps to access APIs from other domains.

39. What is a NuGet Package?

Dependency manager for .NET libraries.

40. What is .NET Standard?

A versioned set of APIs available across all .NET platforms.

41. Explain Sealed Class.

Cannot be inherited, used for security/performance.

42. What is a Partial Class?

A class split into multiple files.

43. What is Reflection?

Inspecting metadata during runtime.

44. What is ADO.NET?

Low-level data access using:

SqlConnection
SqlCommand
SqlDataReader

45. What is Thread and Task in .NET?

Thread → independent execution path
Task → lightweight wrapper for async operations

46. Explain SOLID Principles.

5 design principles for maintainable code:

Single Responsibility
Open Closed
Liskov Substitution
Interface Segregation
Dependency Inversion

47. What is Attribute in C#?

Metadata added to classes or methods.

Example:


[Authorize]
public class HomeController { }

48. What is Filter in ASP.NET Core?

Executes logic before or after controller actions.
Types:

Authorization
Resource
Action
Exception

49. What is Web API Versioning?

Manage multiple versions of APIs for backward compatibility.

50. What is Health Check in ASP.NET Core?

Used to monitor the health of application and services in production.

Saturday, November 22, 2025

🧩 .NET Framework Monolithic to Microservices Conversion Using AI Tools – A Complete Guide

Migrating a .NET monolithic application to a modern microservices architecture is one of the most impactful modernization decisions organizations make today.
With the rise of AI-driven code analysis, automated refactoring tools, and architectural recommendation engines, the process has become faster, safer, and more predictable.

This article explains how to convert a .NET Framework monolith into microservices using AI tools, key considerations, prerequisites, step-by-step approach, and best practices.

🏛 1. Introduction

Most enterprise applications built between 2000 and 2015 were created using the .NET Framework in a monolithic architecture.
These systems often face problems such as:

Tight coupling
Slow deployments
Difficult scalability
Technology lock-in
Hard dependency management
Cannot easily adopt cloud-native patterns

Modernizing them into microservices (.NET 6/7/8+) provides agility, scalability, CI/CD friendliness, and improved fault isolation.

With new advancements in AI-powered tools, monolith-to-microservice conversion is now faster and significantly lower risk.

🤖 2. Role of AI in Monolithic to Microservices Conversion

AI does not "write microservices automatically," but it accelerates and improves the modernization process by:

✔ Understanding legacy code faster

AI can scan millions of lines of code and generate:

Architecture maps
Dependency diagrams
Domain clusters
Coupling reports

✔ Identifying logical microservice boundaries

AI tools perform domain decomposition using:

Domain-driven design principles
Data ownership
Code dependency graphs
API behavior

✔ Suggesting refactoring patterns

AI identifies where to apply:

Repository pattern
Facade pattern
Anti-corruption layer
CQRS
Strangler Fig pattern

✔ Auto-generating cloud-ready .NET Core code

Some tools can rewrite:

ASP.NET WebForms → ASP.NET Core MVC
WCF → gRPC / Web API
ADO.NET → EF Core
Config files → appsettings.json

✔ Recommending infrastructure components

AI suggests best-suited:

Containers
API gateways
Kubernetes settings
Observability framework

🛠 3. Popular AI Tools for .NET Modernization

These tools help accelerate monolith decomposition:

1. Microsoft AppCAT (Application Compatibility & Modernization Tool)

Identifies .NET Framework APIs
Suggests migration fixes
Creates modernization report

2. Azure Migrate – App Containerization

Containerizes legacy .NET apps
Adds Docker configuration
Suggests microservice boundaries

3. IBM Mono2Micro (AI-based decomposition)

AI clustering
Identifies microservices domains
Recommends service boundaries
Generates code transformation hints

4. AWS Microservice Extractor for .NET

Uses static/dynamic analysis
Detects domain boundaries
Generates microservice templates

5. GPT-based Code Analysis (ChatGPT, Copilot)

Can assist in:

Refactoring code
Splitting modules
Creating services
Writing documentation
Generating .NET Core code

🧭 4. Key Points to Keep in Mind Before Converting

✔ 1. Identify business domains (DDD – Domain-Driven Design)

Break application into:

Customer Management
Billing
Payments
Inventory
Reports

✔ 2. Loosely coupled boundaries

Each service should own its data and not depend on others internally.

✔ 3. Data migration strategy

Every microservice must have:

Its own database
No cross-schema joins
Communication via API or messaging

✔ 4. Communication pattern

Choose between:

REST API
gRPC
Event-driven architecture (RabbitMQ, Kafka)

✔ 5. Authentication/Authorization

Use:

IdentityServer
Azure AD / B2C
JWT tokens

✔ 6. Observability

Include:

Logging
Distributed tracing
Metrics
Health checks

✔ 7. Deployment strategy

Adopt:

Docker
Kubernetes
Azure App Services / AKS

📦 5. Step-by-Step Conversion Approach (Using AI Tools)

Step 1: Assess the Monolithic Application

Use tools:

Microsoft AppCAT
AWS Microservice Extractor
IBM Mono2Micro

These generate:

Code dependency graphs
API/service flow
Class coupling
Complexity reports
Recommended service boundaries

Step 2: Identify Microservices Using AI Decomposition

AI clusters business functionality into domains:

Example:

OrderService

Place order
Modify order
Cancel order
Order history

InventoryService

Stock update
Stock reservation
Warehouse management

PaymentService

Payment gateway
Refund
Transactions

AI gives:

Boundary suggestions
Data ownership mapping
APIs extraction recommendations

Step 3: Choose a Migration Pattern

1. Strangler Fig Pattern (Most recommended)

Gradually replace monolith modules with microservices.

2. Rewrite pattern

Rewrite entire application → High risk.

3. Side-by-side modernisation

Build services while monolith still runs.

AI tools help in:

Deciding the correct pattern
Identifying least risky modules
Estimating effort

Step 4: Extract Code for Each Microservice

AI tools help generate:

Controllers
Service classes
DTOs
DbContext
Repositories
Unit tests

Framework target: .NET 6/7/8

Step 5: Build API Gateway

Use:

Ocelot
YARP
Azure API Management

AI can auto-generate:

Policies
Route configuration
JWT validation

Step 6: Containerization Using AI Tools

Azure Migrate or Docker AI can auto-generate:

Dockerfile
Entry point scripts
Kubernetes YAML
Helm charts

Step 7: Data Migration (Per-Service Database)

Split databases using:

Database-per-service
Schema-per-service
Table-per-service

AI suggests optimized schemas and detects foreign key conflicts.

Step 8: Testing and Validation

Use AI for:

Unit test generation
Automated integration test scripts
API contract testing

🧱 6. Real-Time Example: Monolith to Microservice Conversion

Suppose you have a Retail Monolithic App with:

Controllers/
Services/
Repositories/
Database/
UI/

AI tools detect domains:

User Management
Catalog
Orders
Payments
Delivery

Then it generates:

OrderService/
    .NET 8 Web API
    OrderController.cs
    OrderService.cs
    OrderDbContext.cs
    RabbitMQ integration

And integrates it into:

API Gateway → OrderService
Monolith → Catalog

Gradually, each module is replaced.

🛡 7. Common Mistakes to Avoid

❌ Converting entire monolith at once
❌ Sharing database between services
❌ Ignoring distributed transactions
❌ Not implementing centralized logging
❌ Not using versioning for APIs
❌ Overusing synchronous calls

🎯 8. Best Practices

✔ Start with a domain that has least external dependencies
✔ Use Strangler Fig pattern
✔ Implement circuit breakers (Polly)
✔ Maintain backward compatibility
✔ Use asynchronous communication
✔ Keep services small but meaningful
✔ Document everything (AI can help auto-document)

🚀 9. Conclusion

AI-assisted modernization makes monolith-to-microservices conversion:

Faster
Reliable
Predictable
Cost-efficient

By combining AI code analysis, DDD principles, modern .NET Core, and cloud-native tools, organizations can transform legacy .NET Framework applications into scalable, cloud-ready microservices.