.NET Developer Technical Interview Assessment

.NET Developer Technical Interview Assessment

Section 1: Theoretical Questions (45 minutes)

.NET Core Fundamentals

1. Explain the key differences between .NET Framework and .NET Core. Why might you choose one over the other for a fintech application?
2. Describe the middleware pipeline in ASP.NET Core and how you would implement custom middleware.
3. How does dependency injection work in .NET Core? Provide examples of how you've used it in previous projects.
4. Explain the concept of middleware in ASP.NET Core and how it differs from HTTP modules in earlier versions.
5. What are the benefits of using a generic host in .NET Core applications?

Web API Development

6. Describe RESTful API design best practices. How would you implement versioning in a Web API?
7. Explain the role of filters in ASP.NET Core Web API. Provide examples of when you might use action filters versus exception filters.
8. How would you implement authentication and authorization in a Web API for a fintech application? Discuss OAuth 2.0 and JWT implementation.
9. Describe how you would handle cross-origin requests (CORS) in a Web API.
10. Explain the difference between PUT and PATCH HTTP methods and when you would use each.

Entity Framework & SQL

11. Compare and contrast the Code-First and Database-First approaches in Entity Framework. When would you choose one over the other?
12. Explain the concept of tracking in Entity Framework and its performance implications.
13. How would you optimize a complex SQL query that's performing poorly? Provide specific examples of techniques you've used.
14. Describe the different types of relationships in Entity Framework (one-to-one, one-to-many, many-to-many) and how you would implement them.
15. How would you handle database migrations in a production environment with minimal downtime?

Microservices & Event-Driven Architecture

16. Explain the advantages and challenges of implementing a microservices architecture for a fintech platform.
17. Describe how you would implement message queuing in a distributed system. Which technologies have you used?
18. How would you handle data consistency across microservices in a financial application?
19. Explain the concept of event sourcing and when it might be appropriate to use it in a fintech application.
20. How would you implement service discovery in a microservices architecture?

Azure & CI/CD

21. Describe the Azure services you've used for hosting .NET applications. What are the benefits of each?
22. Explain how you would implement auto-scaling for a .NET application in Azure.
23. How would you set up a CI/CD pipeline for a .NET Core application using Azure DevOps?
24. Describe strategies for monitoring and logging in a production Azure environment.
25. How would you handle secrets management in an Azure-hosted application?

Section 2: Coding Assessment (90 minutes)

Task 1: API Development

Create a simple ASP.NET Core Web API for a basic payment processing system with the following requirements:

• Implement endpoints for:
  • Creating a payment transaction
  • Retrieving transaction details
  • Listing transactions with filtering and pagination
• Include proper validation and error handling
• Implement appropriate authentication using JWT
• Include unit tests for your controllers
• Use Entity Framework Core for data access

Task 2: Microservice Communication

Implement a simple event-driven system with two microservices:

1. Transaction Service:

   • Processes payment transactions
   • Publishes events when transactions are created or updated

2. Notification Service:

   • Subscribes to transaction events
   • Sends notifications based on transaction status changes

Use Azure Service Bus or RabbitMQ for message queuing.

Task 3: Database Design & Performance

Design a database schema for a financial transaction system with the following requirements:

• Support for multiple account types
• Transaction history with detailed metadata
• Efficient querying for transaction reporting
• Proper indexing strategy

Write a complex LINQ query to retrieve transactions with specific criteria and explain your approach to optimizing it.

Section 3: System Design Exercise (45 minutes)

Scenario: Design a Fintech Payment Gateway

Design a scalable, secure payment gateway system that can handle high transaction volumes with the following requirements:

• Support for multiple payment methods (credit cards, bank transfers, digital wallets)
• Real-time transaction processing
• Secure storage of sensitive payment information
• Integration with external payment providers
• Compliance with financial regulations (PCI-DSS, etc.)
• High availability and disaster recovery
• Monitoring and alerting system

Your design should include:

1. System architecture diagram
2. Component descriptions
3. Data flow explanation
4. Scalability considerations
5. Security measures
6. Deployment strategy on Azure

Section 4: Code Review Exercise (30 minutes)

Review the following code snippet from a financial application and identify potential issues, improvements, and security concerns:

public class PaymentController : ControllerBase
{
    private readonly string _connectionString = "Server=myserver;Database=payments;User Id=admin;Password=password123;";
    
    [HttpPost("process")]
    public async Task<IActionResult> ProcessPayment(PaymentRequest request)
    {
        if (request == null)
            return BadRequest();
        
        using (var connection = new SqlConnection(_connectionString))
        {
            await connection.OpenAsync();
            var command = new SqlCommand(
                "INSERT INTO Transactions (AccountId, Amount, Description) VALUES (@AccountId, @Amount, @Description)",
                connection);
            
            command.Parameters.AddWithValue("@AccountId", request.AccountId);
            command.Parameters.AddWithValue("@Amount", request.Amount);
            command.Parameters.AddWithValue("@Description", request.Description);
            
            await command.ExecuteNonQueryAsync();
        }
        
        // Send confirmation email
        var smtpClient = new SmtpClient("smtp.company.com");
        smtpClient.Send("system@company.com", request.Email, "Payment Confirmation", 
            $"Your payment of {request.Amount} was processed successfully.");
        
        return Ok(new { Success = true, Message = "Payment processed" });
    }
    
    [HttpGet("transactions")]
    public List<Transaction> GetTransactions()
    {
        var transactions = new List<Transaction>();
        using (var connection = new SqlConnection(_connectionString))
        {
            connection.Open();
            var command = new SqlCommand("SELECT * FROM Transactions", connection);
            
            using (var reader = command.ExecuteReader())
            {
                while (reader.Read())
                {
                    transactions.Add(new Transaction
                    {
                        Id = (int)reader["Id"],
                        AccountId = (int)reader["AccountId"],
                        Amount = (decimal)reader["Amount"],
                        Description = (string)reader["Description"],
                        CreatedAt = (DateTime)reader["CreatedAt"]
                    });
                }
            }
        }
        
        return transactions;
    }
}

Evaluation Criteria

Candidates will be evaluated on:

1. Technical knowledge and experience with .NET Core, ASP.NET, and related technologies
2. Understanding of database design and optimization principles
3. Experience with microservices and event-driven architectures
4. Familiarity with Azure cloud services and CI/CD practices
5. Code quality, including structure, readability, and error handling
6. Problem-solving approach and architectural thinking
7. Communication skills and ability to explain technical concepts
8. Knowledge of security best practices for financial applications
9. Experience with performance optimization techniques