1. Factory Pattern vs. Abstract Factory Pattern

Question: Can you explain the difference between the Factory Method and Abstract Factory patterns? When would you use one over the other?

Explanation: Factory Method allows the creation of objects without specifying the exact class of the object to be created, while Abstract Factory provides an interface for creating families of related objects. The latter is useful for systems that need to work with multiple families of products, while Factory Method suits single-object creation scenarios.

2. Dependency Injection vs. Service Locator

Question: What is the difference between Dependency Injection (DI) and the Service Locator pattern? When is DI preferred?

Explanation: Dependency Injection injects dependencies into objects, promoting loose coupling, while Service Locator is a registry that allows objects to look up their dependencies. DI is generally preferred in modern development due to its transparency and testability, but Service Locator might still be useful in legacy code or frameworks that lack DI support.

3. Repository Pattern vs. Data Access Object (DAO) Pattern

Question: How does the Repository pattern differ from the DAO pattern? When would you choose one over the other?

Explanation: Both patterns abstract data access logic, but the Repository pattern provides a collection-like interface for domain objects, often closer to business logic. DAO, on the other hand, directly interacts with the database. Repository is more useful in DDD (Domain-Driven Design) contexts, while DAO is suited for data-centric applications.

4. Solid Principles (Single Responsibility Principle)

Question: Can you explain the Single Responsibility Principle (SRP) and provide an example of how violating SRP can cause problems in .NET?

Explanation: SRP states that a class should have only one reason to change. Violating SRP can make classes harder to maintain, test, and scale. For instance, if a UserService handles both business logic and data access, it would be harder to refactor or extend compared to separating responsibilities into distinct classes.

5. CQRS (Command Query Responsibility Segregation)

Question: What is CQRS, and how does it differ from the traditional CRUD approach? When is CQRS beneficial?

Explanation: CQRS separates read and write responsibilities into different models, allowing more optimized queries and scalability. Unlike CRUD, which treats all operations similarly, CQRS is beneficial for high-read systems or those needing more complex data handling.

6. Microservices vs. Monolith Architecture

Question: How would you approach breaking down a monolithic application into microservices? What are the main considerations?

Explanation: Considerations include data ownership, inter-service communication, transaction handling, and deployment complexity. Breaking down by business boundaries (bounded contexts) is generally recommended. It’s crucial to ensure each service is independently deployable, scalable, and loosely coupled.

7. State Management in .NET (In-Memory Cache vs. Distributed Cache)

Question: When would you use an in-memory cache vs. a distributed cache in a .NET application?

Explanation: In-memory cache (e.g., MemoryCache) is fast but limited to a single instance, ideal for session data in smaller applications. Distributed caches (e.g., Redis) are better for larger applications or cloud environments where multiple instances require shared state.

8. Asynchronous Programming vs. Multithreading in .NET

Question: What is the difference between asynchronous programming (async/await) and multithreading in .NET? When would you use one over the other?

Explanation: Asynchronous programming allows non-blocking operations and is used mainly for I/O-bound tasks. Multithreading is beneficial for CPU-bound tasks. Understanding this distinction is critical for optimizing performance in .NET applications.

9. Event-Driven Architecture vs. Message-Driven Architecture

Question: How do you distinguish between event-driven and message-driven architectures? Which would you choose in a microservices context?

Explanation: Event-driven systems use events to trigger responses, often asynchronously. Message-driven systems emphasize message-passing, typically with more robust guarantees and can involve synchronous or asynchronous processing. Event-driven is often favored in microservices for flexibility, while message-driven is preferred when reliability or ordering is essential.

10. Pros and Cons of Using ORM (e.g., Entity Framework)

Question: What are the benefits and potential pitfalls of using an ORM like Entity Framework in .NET? When might you choose a custom data access layer instead?

Explanation: ORMs simplify database operations with object mapping but can lead to inefficiencies like excessive queries (N+1 problem). Custom data access layers offer greater control and can improve performance in complex systems where ORM limitations become problematic.

11. Unit Testing vs. Integration Testing

Question: What is the difference between unit testing and integration testing, and how do you ensure that each type is effective in a .NET application?

Explanation: Unit tests focus on isolated code segments, while integration tests validate the interaction between components. For effectiveness, ensure unit tests cover business logic comprehensively, while integration tests verify end-to-end workflows. Tools like MSTest or xUnit for unit testing, and a testing framework like SpecFlow for integration testing, are popular in .NET.

12. Circuit Breaker Pattern in .NET

Question: What is the Circuit Breaker pattern, and how does it help improve system resilience in a .NET application?

Explanation: Circuit Breaker prevents repeated failed calls to an unstable service, "breaking" the connection after a certain threshold to avoid overwhelming it. Tools like Polly in .NET facilitate its implementation, especially useful in microservices for fault tolerance.

These topics are highly relevant for senior or lead roles, where understanding complex design decisions, trade-offs, and architectural principles is essential. Each question helps interviewers gauge not only technical depth but also design foresight, system resilience, and maintainability considerations.