Are you looking for a .NET developer job and preparing for a tech interview? To help you succeed, we’ve compiled a list of 13 advanced ASP.NET Core interview questions and answers that cover a wide range of topics, such as ASP.NET Core, C#, concurrency, parallelism, and more.
These questions are designed to test your knowledge and understanding of advanced concepts and features of the ASP.NET Core framework. So, whether you’re an experienced developer or just starting your career in .NET, these questions will help you prepare for your interview and stand out from the crowd.
1. What’s the difference between .NET and .NET Framework?
.NET (previously .NET Core) and .NET Framework are both web development frameworks for building applications using the .NET technology stack. However, the two have some key differences.
.NET is an open-source, cross-platform framework with core libraries (in NuGet packages) for building modern, cloud-based, and microservices-based applications. It supports development on Linux, macOS, and Windows and provides a modular lightweight runtime deployed as a self-contained executable or a shared library.
.NET Framework, on the other hand, is a Windows-only framework for developing classes and libraries and running code on web services and traditional desktop applications. It provides a larger set of libraries and features than .NET Core, but it’s limited to Windows and is not open-source.
2. How does ASP.NET Core handle dependency injection?
Dependency injection is a design pattern of ASP.NET Core that’s handled by the built-in dependency injection container. This container can register and resolve dependencies, typically defined as interfaces implemented by concrete classes.
There are several ways to configure the container, including the ConfigureServices method in the Startup class (the entry point of a .NET application), attributes on classes and properties, and the service provider itself. ASP.NET Core supports constructor, property, and method injection, allowing dependencies to be dynamically injected into methods at runtime.
However, a more up-to-date way to handle dependency injection in ASP.NET Core focuses on singleton, transient, and scoped service lifetimes. You can read more about this here.
3. What is Kestrel and how does it differ from IIS?
Kestrel is a cross-platform, lightweight web server used by default in ASP.NET Core applications. It can run on Linux, macOS, and Windows and provides a fast, scalable, and efficient platform for handling HTTP requests.
Kestrel is designed to be used with a reverse proxy server, such as IIS or Nginx, which handles load balancing and SSL termination tasks.
On the other hand, IIS is a web server specific to Windows that provides more advanced features than Kestrel, such as support for HTTP/2 and WebSocket protocols and integration with Windows authentication and SSL.
4. What is the purpose of middleware in ASP.NET Core?
Middleware in ASP.NET Core is a software component responsible for processing requests and generating responses in the web application pipeline. It sits between the server side and the application and is designed to handle cross-cutting concerns, such as authentication, caching, logging, and routing.
The primary purpose of middleware is to provide a modular way of processing HTTP requests and responses, allowing developers to add, remove, or reorder middleware components in the pipeline based on their specific needs. This makes it easy to customize the web application's behavior without modifying the core application logic.
In addition, middleware can perform various tasks, such as modifying request or response headers, handling errors and exceptions, and executing asynchronous code. Middleware can also perform custom processing of requests and responses, such as generating dynamic content or formatting data.
Overall, middleware plays a critical role in the architecture of ASP.NET Core applications, allowing developers to write modular, flexible, and extensible web applications that can be easily customized and scaled.
5. How does ASP.NET Core handle garbage collection?
Garbage collection in ASP.NET Core automatically manages the allocation and deallocation of memory that an ASP.NET Core application uses. The garbage collector is responsible for identifying and reclaiming memory no longer needed by the application, thus freeing up resources and improving the application's performance.
The garbage collector in ASP.NET Core uses a generational garbage collection algorithm that divides the heap into gen0, gen1, and gen2, each generation representing a different stage of the object's life cycle. New objects are allocated to the youngest generation, and as they survive longer, they are moved to older generations. The garbage collector collects and frees memory from the youngest generation first and only collects the older generations when necessary.
ASP.NET Core provides several options for configuring and tuning the garbage collector, including setting the maximum size of the heap, the size of the individual generations, and the frequency of garbage collection. These options can be configured using environment variables or application configuration files depending on the needs of the application.
In addition, ASP.NET Core provides several tools and APIs for monitoring and diagnosing garbage collection behavior, including the GC.Collect() method, which can force a garbage collection cycle, and the GC.GetTotalMemory() method, which returns the total amount of memory used by the application.
Overall, garbage collection in ASP.NET Core is a critical component of the runtime, ensuring efficient memory use and improving the performance and stability of ASP.NET Core applications.
6. What’s the difference between synchronous and asynchronous programming in ASP.NET Core?
Synchronous programming in ASP.NET Core blocks the execution of source code until a task is completed. In contrast, asynchronous programming allows the execution of code to continue while a task is being processed in the background.
Asynchronous programming is useful for long-running operations that would otherwise block the application's main thread, such as reading from a file or making a network request.
Asynchronous programming is typically achieved using the async and await keywords in C#. The async keyword defines an asynchronous method, which can be called by other code and will run in the background. The await keyword indicates that the calling code should wait for the asynchronous method to complete before continuing.
7. How does .NET support cross-platform development?
.NET (.NET Core) was designed from the ground up to support cross-platform development. It provides a common runtime, libraries, and tools that can be used to build, debug, and deploy applications on Windows, macOS, and Linux. One of the key components of cross-platform development in .NET is the .NET runtime, which provides a platform-agnostic environment for running .NET applications. The runtime is available on multiple platforms and can be installed independently of the operating system.
Additionally, ASP.NET Core includes a command-line interface (CLI) that can be used to build, test, and deploy applications on multiple platforms. The CLI provides a set of tools for managing dependencies, building and packaging applications, and deploying them to different environments. ASP.NET Core also includes a set of standard libraries called the Base Class Library (BCL), which provide a consistent set of APIs for working with common tasks, such as file I/O, networking, and security.
These libraries are designed to work on multiple platforms and provide a consistent experience for developers across different environments. Overall, .NET's support for cross-platform development makes it a powerful tool for building modern, cloud-based, and microservices-based applications that can run on various operating systems and environments.
8. How can you implement background work in an ASP.NET Core application?
The IHostedService interface in ASP.NET Core defines a background task or service as part of the application's lifetime. It’s typically used for monitoring, logging, or data processing tasks that must run continuously, even when the application is not processing requests. Classes that implement the IHostedService interface are added to the application's service collection using dependency injection, and they are started and stopped automatically by the application's host.
The IHostedService interface defines two methods: StartAsync and StopAsync. The StartAsync method is called when the application starts and is used to start the background task or service. The StopAsync method is called when the application is stopped or restarted. It’s used to stop the background task or service, releasing acquired resources.
9. How does ASP.NET Core handle concurrency and parallelism?
ASP.NET Core provides several mechanisms for handling concurrency and parallelism depending on the application's specific requirements. Some common mechanisms used in ASP.NET Core applications are:
- Asynchronous programming: ASP.NET Core supports asynchronous programming by using the async and awaits keywords. Asynchronous programming allows multiple tasks to be executed concurrently without blocking the main thread, improving the application's responsiveness.
- Parallel programming: ASP.NET Core supports parallel programming using the Parallel class and the Task Parallel Library (TPL). Parallel programming allows multiple tasks to be executed concurrently across multiple processors, improving the application's performance.
- Locking and synchronization: ASP.NET Core provides several mechanisms for locking and synchronization, including the lock keyword, the Interlocked class, and the Monitor class. These mechanisms allow multiple threads to access shared resources safely and prevent race conditions.
- Concurrency control: ASP.NET Core supports concurrency control through transactional memory and the optimistic concurrency control (OCC) pattern. Concurrency control ensures that multiple threads can access and modify shared resources without interfering with each other.
Using these mechanisms, developers can build ASP.NET Core applications that are more responsive, scalable, and efficient, handling multiple requests and tasks concurrently and in parallel. However, using these mechanisms carefully and appropriately is important, as concurrency and parallelism can introduce new challenges, such as race conditions, deadlocks, and thread starvation.
10. How do you implement caching in ASP.NET Core?
Response caching in ASP.NET Core is a technique used to improve the performance and scalability of web applications by caching the ASP.NET Core MVC responses returned by the server for a specific period. Caching the response can help reduce the number of requests made to the server, as clients can reuse the cached response instead of requesting the same resource again.
Response caching works by adding a caching layer between the client and the server. When a client requests a resource, the caching layer checks whether the response for the request has been cached. If the response is cached, the caching layer returns the cached response to the client. If the response is not cached, the request is forwarded to the server, and the server generates the response and caches it for future use.
In ASP.NET Core, response caching can be implemented using the [ResponseCache] attribute, which can be applied to an action method in a controller. The attribute allows developers to specify the caching behavior, such as the duration of the cache, the location of the cache, and the cache key. By default, the caching location is on the client side, but it can also be set to a distributed or proxy cache depending on the needs of the application.
Response caching can significantly impact the performance and scalability of web applications, particularly for resources that are expensive to generate, such as database queries or API calls. However, it’s important to use response caching judiciously, as caching can also lead to stale data being returned to clients. Therefore, setting appropriate caching policies and ensuring the cache is invalidated when the underlying data changes are crucial.
11. What’s the difference between middleware and a filter in ASP.NET Core?
In ASP.NET Core, middleware and filters are two mechanisms used for processing requests and responses.
Middleware is a software component between the web server (like Apache) and the application and processes requests and responses during the application development. Middleware can be used for various tasks, such as authentication, logging, and error handling. Middleware is executed in a pipeline, and each middleware component can modify the request or response before passing it to the next component in the pipeline.
Conversely, filters are used to perform cross-cutting concerns on controllers and actions in an MVC application. Filters can be used for authorization, validation, and caching tasks. Filters are executed before and after the action method, and they can modify the request or response or short-circuit the request processing if necessary.
The main difference between middleware and filters is their scope and the way they are executed. Middleware is executed globally and can be used for any request or response. In contrast, filters are executed only for specific controllers or actions and can be used to modify the request or response before or after the action method.
12. What is Core CLR?
CoreCLR (Common Language Runtime, now renamed to .NET Runtime) is the runtime environment executing ASP.NET Core applications. It is the open-source implementation of the .NET runtime, developed by Microsoft and available on multiple platforms, including Windows, Linux, and macOS.
CoreCLR provides a managed execution environment for ASP.NET Core applications, including memory management, garbage collection, type safety, and security. It also supports just-in-time (JIT) compilation, which compiles code at runtime to native machine code, allowing for faster execution.
CoreCLR is designed to be modular, with various components such as the garbage collector, JIT compiler, and primitive data type system implemented as separate modules. This modularity allows for more flexibility and customization in building and deploying .NET Core applications.
CoreCLR is a critical component of the .NET platform, providing the necessary runtime infrastructure for developing and executing .NET applications across different platforms.
13. Have you worked with Docker on ASP.NET Core projects?
The Docker platform allows developers to package and deploy applications in lightweight, portable containers. In the context of ASP.NET Core, Docker provides a way to package and deploy ASP.NET Core applications and their dependencies in a self-contained, isolated container that can run on any platform that supports Docker.
Using Docker in ASP.NET Core, developers can create Docker images of their applications, which can be deployed to any environment that supports Docker. This makes it easy to deploy ASP.NET Core applications consistently and reliably, without worrying about differences in the underlying infrastructure.
Docker also provides a way to manage and orchestrate containers in a distributed system, allowing developers to scale their applications up or down as needed.
Overall, Docker is a powerful tool for developing, deploying, and managing ASP.NET Core applications, providing a portable, flexible, and scalable environment for building modern applications.
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