Senior .NET Software Engineer Interview Preparation: Complete Topic Checklist

1. Advanced C# and .NET Fundamentals

• Object-Oriented Programming (OOP)
• SOLID principles
• Classes, structs, records, and interfaces
• Abstract classes vs. interfaces
• Value types vs. reference types
• Stack vs. heap fundamentals
• Generics and generic constraints
• Delegates, events, and lambda expressions
• LINQ and deferred execution
• IEnumerable<T> vs. IQueryable<T>
• Extension methods
• Nullable reference types
• Boxing and unboxing
• Exception handling and custom exceptions
• Garbage collection and memory management
• IDisposable and IAsyncDisposable
• Reflection and attributes
• C# records, pattern matching, and modern language features

2. Asynchronous Programming and Concurrency

• async and await
• Task and Task<T>
• Task.WhenAll() and Task.WhenAny()
• Task vs. Thread
• CPU-bound vs. I/O-bound operations
• Thread pool
• Cancellation tokens
• async void and common pitfalls
• Race conditions
• Deadlocks
• Locks and synchronization
• SemaphoreSlim and Monitor
• Thread-safe collections
• ConcurrentDictionary
• Parallel programming
• Bounded concurrency
• Thread safety in ASP.NET Core applications

3. ASP.NET Core and Web API

• ASP.NET Core request pipeline
• Middleware and middleware ordering
• Dependency injection
• Singleton, scoped, and transient lifetimes
• Controllers vs. Minimal APIs
• Routing and model binding
• Model validation
• Action filters and endpoint filters
• Custom middleware
• Global exception handling
• RESTful API design
• HTTP methods and status codes
• Idempotency
• API versioning
• Pagination, filtering, and sorting
• Rate limiting
• Response caching
• Health checks
• Configuration and environment variables
• Options pattern
• Logging and structured logging
• Swagger and OpenAPI
• Background services and hosted services

4. Entity Framework Core

• Code-first vs. database-first approaches
• DbContext lifecycle and dependency injection
• Change tracking vs. AsNoTracking()
• IQueryable<T> vs. IEnumerable<T>
• Eager, lazy, and explicit loading
• Include() and ThenInclude()
• Projection with Select()
• The N+1 query problem
• Query translation and generated SQL
• Migrations and schema management
• Transactions
• Optimistic concurrency
• Concurrency tokens and row versioning
• Relationships and navigation properties
• Owned entity types
• Global query filters
• Compiled queries
• Bulk updates and deletes
• EF Core performance optimization
• DbContext thread safety
• Connection pooling
• Repository and Unit of Work patterns with EF Core

5. SQL Server and Database Fundamentals

• SELECT queries and filtering
• INNER, LEFT, RIGHT, and FULL JOIN
• GROUP BY and HAVING
• Subqueries and common table expressions (CTEs)
• Window functions
• Stored procedures and functions
• Views and triggers
• Primary and foreign keys
• Database normalization and denormalization
• Clustered and nonclustered indexes
• Composite and covering indexes
• Index fragmentation fundamentals
• Query execution plans
• Query optimization
• Transactions and ACID properties
• Isolation levels
• Locking and blocking
• Deadlocks and troubleshooting
• Optimistic vs. pessimistic concurrency
• Database partitioning
• Pagination strategies
• Connection pooling
• Database backup and recovery fundamentals

6. Software Architecture and Design Patterns

• SOLID principles in real-world applications
• Clean Architecture
• Layered architecture
• Hexagonal architecture
• Vertical slice architecture
• Domain-Driven Design (DDD)
• Dependency inversion
• Dependency injection
• Separation of concerns
• Repository pattern
• Unit of Work pattern
• Factory pattern
• Strategy pattern
• Decorator pattern
• Adapter pattern
• Observer pattern
• Mediator pattern
• CQRS
• Event-driven architecture
• Modular monoliths
• Microservices architecture
• Monolith vs. microservices
• Domain models and domain services
• Maintainability, extensibility, and testability
• Architectural trade-offs

7. System Design and Distributed Systems

• Functional and nonfunctional requirements
• Scalability and availability
• Vertical vs. horizontal scaling
• Load balancing
• Stateless application design
• API gateways
• Database replication
• Database partitioning and sharding
• Distributed caching
• Redis fundamentals
• Message queues
• Publish/subscribe architecture
• Eventual consistency
• CAP theorem fundamentals
• Idempotent operations
• Retries and exponential backoff
• Timeouts and circuit breakers
• Bulkhead isolation
• Distributed transactions
• Transactional outbox pattern
• Saga pattern fundamentals
• Duplicate message handling
• Service-to-service communication
• Fault tolerance and recovery

8. Authentication and Application Security

• Authentication vs. authorization
• JWT authentication
• OAuth 2.0
• OpenID Connect
• Claims-based authorization
• Role-based authorization
• Resource-based authorization
• Access tokens and refresh tokens
• Password hashing and secure credential storage
• HTTPS and TLS fundamentals
• SQL injection prevention
• Cross-site scripting (XSS)
• Cross-site request forgery (CSRF)
• Broken access control
• Server-side request forgery (SSRF)
• Input validation and output encoding
• Secrets management
• Least privilege
• Secure API design
• Rate limiting and brute-force protection
• Security headers
• Dependency and vulnerability management
• Secure logging and audit trails
• OWASP Top 10

9. Testing and Code Quality

• Unit testing
• Integration testing
• End-to-end testing
• API testing
• Contract testing
• Performance and load testing
• xUnit and NUnit
• Mocking frameworks such as Moq
• Test doubles: mocks, stubs, and fakes
• Arrange–Act–Assert pattern
• Test-driven development (TDD)
• Behavior-driven development (BDD) fundamentals
• ASP.NET Core integration testing
• Test fixtures and test data
• Database testing
• Code coverage and its limitations
• Regression testing
• Static code analysis
• Refactoring and code smells
• Testable architecture

10. Performance Optimization and Troubleshooting

• CPU and memory profiling
• Garbage collection and allocation optimization
• Memory leaks
• Object lifetime management
• Database query profiling
• EF Core performance optimization
• Asynchronous I/O
• Thread pool starvation
• Connection pool exhaustion
• Caching strategies
• Cache invalidation
• Response compression
• Pagination and data projection
• HTTP performance
• Latency and throughput
• Load testing
• Bottleneck identification
• Production debugging
• Root cause analysis
• Performance regression investigation

11. Messaging and Background Processing

• Background services in ASP.NET Core
• IHostedService and BackgroundService
• Scheduled jobs
• Queue-based processing
• RabbitMQ fundamentals
• Azure Service Bus fundamentals
• Amazon SQS fundamentals
• Message acknowledgment
• Delivery guarantees
• At-most-once and at-least-once delivery
• Idempotent consumers
• Retry policies
• Dead-letter queues
• Transactional outbox pattern
• Event-driven workflows
• Handling failed messages
• Long-running task processing

12. Cloud, Docker, and DevOps

• Docker fundamentals
• Dockerfile and image layers
• Multi-stage Docker builds
• Container networking
• Container security
• Environment-specific configuration
• Docker Compose
• CI/CD pipelines
• Automated builds and tests
• Deployment strategies
• Rollbacks and release management
• Database migration strategies
• Azure App Service and Azure SQL
• Azure Functions and Azure Service Bus
• Azure Key Vault and Application Insights
• AWS ECS, RDS, Lambda, SQS, and CloudWatch
• Cloud storage and managed databases
• Secrets and configuration management
• Infrastructure as Code fundamentals

13. Logging, Monitoring, and Observability

• Structured logging
• Logging levels
• Microsoft.Extensions.Logging
• Serilog fundamentals
• Correlation IDs
• Distributed tracing
• Metrics and dashboards
• OpenTelemetry
• Application health checks
• Exception monitoring
• Alerting and incident response
• Centralized log aggregation
• Performance monitoring
• Service-level indicators (SLIs)
• Service-level objectives (SLOs)
• Production diagnostics

14. Git and Engineering Workflow

• Git branching strategies
• Merge vs. rebase
• Resolving merge conflicts
• Pull requests and code reviews
• Commit hygiene
• Release and version management
• Semantic versioning
• NuGet package management
• Dependency management
• Build troubleshooting
• CI pipeline troubleshooting
• Technical documentation
• Code review standards

15. Coding and Problem-Solving

• Arrays and strings
• Dictionaries and hash sets
• Stacks and queues
• Linked lists
• Trees and graphs
• Sorting and searching
• Recursion
• Binary search
• Two-pointer techniques
• Sliding window
• Hashing and frequency counting
• Time and space complexity
• Big-O notation
• LINQ coding exercises
• Collection transformations
• Async programming exercises
• Thread-safe implementations
• Practical refactoring problems
• Debugging and optimizing existing code

16. Senior-Level Leadership and Behavioral Topics

• Technical decision-making
• Architecture reviews
• Code review and mentoring
• Breaking down complex requirements
• Technical debt management
• Refactoring legacy systems
• Production incident management
• Root cause analysis
• Cross-team collaboration
• Communicating technical trade-offs
• Conflict resolution
• Estimation and risk management
• Prioritization under deadlines
• Balancing quality and delivery
• Taking ownership of features
• Designing for maintainability
• Knowledge sharing and technical documentation

17. Practical System Design Exercises

Practice designing the architecture and explaining the trade-offs for:

• E-commerce order management system
• High-traffic REST API
• Authentication and authorization service
• URL shortener
• Notification service
• Inventory management system
• Payment processing workflow
• Background job processing system
• Healthcare data API
• Logging and monitoring platform

For each exercise, consider API contracts, database schema, data consistency, security, scalability, caching, failure handling, testing, and deployment.

Final Checklist

Prioritize advanced C#, ASP.NET Core, SQL Server, EF Core, software architecture, security, and system design. Then strengthen your knowledge of testing, performance, distributed systems, cloud infrastructure, and technical leadership.

A senior-level interview is not just a test of definitions. Be prepared to explain how each concept works, when you would use it, what can go wrong, and which alternatives you would consider in a real production system.