ASP.NET

 

ASP.NET

Q1: Diff Transient, Scoped, and Singleton service lifetimes?

• Transient: Created every time. Good for lightweight, stateless services.
• Scoped: Created 1/client request (connection). Any API or web request sharing same HTTP context shares exact same instance.
• Singleton: Only single, identical instance thru app's lifecycle.

Q2: State Management

1) ViewState (Client-Side)

• How: Serializes data into hidden HTML input field (__VIEWSTATE).
• Scope: Single page postbacks.
• Trade-off: Saves server RAM. Hvy network payloads slow page loads. Legacy (Web Forms).

2) Cookies (Client-Side)

• How: Text files in browser sent automatically with every HTTP request.

• Scope: Across requests until expiration.
• Trade-off: Great for user preferences. Vulnerable to tampering. Max 4KB size.

3) Query Strings (Client-Side)

• How: Appends key-value pairs to URL end (?id=123).

• Scope: Single targeted HTTP request.

• Trade-off: Easy setup. Shareable/bookmarkable. Insecure; data visible in address bar.

• 4) Session State (Server-Side)

  • How: Stores data on server. Links client via unique Session ID cookie.

  • Scope: Single user across active browser session.

  • Trade-off: Secures data. Consumes server RAM unless offloaded to Redis/SQL.

5) App State (Server-Side)

• How: Global variables put in server memory (HttpAppState).

• Scope: All users, all requests.

• Trade-off: Perfect for global config. Requires locks (Lock/Unlock) to avoid thread collision.

Q3: MVC Lifecycle (7 Core Events)

1. Routing - UrlRoutingModule gets HTTP request, parses URL, matches route table patterns, extracts controller/action names.

2. Route Handler - Extracts MvcRouteHandler. Creates request context. Instantiates MvcHandler to run pipeline.

3. Controller Factory - MvcHandler calls DefaultControllerFactory. Uses reflection to find, load, instantiate target controller.

4. Actions - ActionInvoker triggers. Binds model inputs. Runs authorization filters. Runs C# controller method.

5. Results - Controller method returns ViewResult, JsonResult.

6. View Engine - Locates .cshtml file (usually via Razor). Compiles layout. Injects controller data into raw HTML.

7. Response - Pushes final HTML/JSON stream to HTTP response pipeline. Sends packet to browser. Ends lifecycle.

Q4: Diff ViewData, ViewBag, and TempData in MVC.

• ViewData: ViewDataDictionary child stores in Key/Value objects so must cast.

• ViewBag: ViewData wrapper rids type casting but no compile-time type safety.

• TempData: TempDataDictionary child that persists data until it is read.

Q4: Role of Kestrel web server and why paired with IIS or Nginx?

• Kestrel: Fast, cross-platform HTTP server built natively into ASP.NET Core to process raw Asynch requests.

• Edge Security: Kestrel lacks auto SSL mgmt, request throttling, and complex load balancing.

• Reverse Proxy Pairing: IIS or Nginx route clean requests to Kestrel.

Q5: Diff IEnumerable and IQueryable in EF Core.

• IEnumerable: Queries DB and pulls all data into server memory. Later filters done in-memory.

• IQueryable: Lazy running of queries. Applies filters (Where, Take) at DB before running SQL.

Q6: Fix SQL Injection and Cross-Site Request Forgery attacks?

• SQL Injection: Use EF Core params or FromSqlRaw to stop malicious string concat.

• CSRF Mitigation: Use [ValidateAntiForgeryToken] or global auto-validation middleware. Razor forms should have hidden anti-forgery token via standard tag helpers.

Q7: "N+1 Query Problem" in EF Core and how fix?

• Problem: App queries Invoice and then Invoice Line Item in a loop.

• Cause: Over rely on Lazy Loading causes lots of unexpected SQL trips per Invoice Line Item.

• Solution: Eager Load via the .Include() and .ThenInclude() to join tables and fetch all data in one SQL.

Q8: How Asynch (async/await) scales?

• Thread Conservation: Stops thread starvation by releasing active thread back to thread pool while waiting for I/O or DB calls.

• Throughput Boost: While external I/O task runs, thread handles other web requests.

• Important: Asynch not faster; but increases the total volume of simultaneous requests the server can manage.

Q9: Tag Helpers and how differ from HTML Helpers?

• Tag Helpers: Server-side C# code in creating and rendering HTML elements in Razor files. Looks like standard HTML tags (e.g., <a asp-controller="Home">).

• HTML Helpers: Rendered as raw C# method invocations mixed into the HTML markup (e.g., @Html.ActionLink("Home", "Index")).

• Advantages: Clean syntax, integrates with front-end tooling, and IntelliSense.

Q10: Content Negotiation in ASP.NET Core Web API, and how work?

• Definition: Server picks the best format (JSON or XML) to return.

• Mechanism: Server inspects the incoming Accept header sent by the client's HTTP request.

• Default: ASP.NET Core defaults to JSON output. Configure the XML serializer in Program.cs using .AddXmlSerializerFormatters() to support XML requests.

Q11: Model Binding and Validation.

• Model Binding: Auto maps HTTP request data (query strings, route data, form fields, or request bodies) into controller action params.

• Validation: Uses [Required] or [StringLength] applied directly to DTO properties.

• Evaluation: Tracks validation status in ModelState.IsValid. In Web APIs decorated with [ApiController], failed validation triggers 400 Bad Request response.

Q12: How handle Dev, Staging, Prod configs?

• Environ Variable: ASPNETCORE_ENVIRONMENT .

• JSON Files: Configs load hierarchically from matching files like appsettings.json and appsettings.Development.json.

• Overriding Rule: Environ-specific JSON file overwrites dup keys found in base config.

Q13: "Options Pattern" and IOptions, IOptionsSnapshot, and IOptionsMonitor?

• Options Pattern: Groups, validates, and injects related config settings via DI.

• IOptions: Singleton. Reads configs once in startup and never updates until the app restarts.

• IOptionsSnapshot: Scoped lifecycle. Reevaluates configs on every new HTTP request.

• IOptionsMonitor: Singleton. Deliver real-time config changes via an OnChange event notifier.

Q14: Structured Logging and why better than flat text logs?

• Structured Logging: Creates key-value pairs inside JSON or other instead of a flat string.

• Flat Text Drawback: Parsing flat text files requires complex reg ex.

• Search Advantage: Log analysis systems (like Serilog paired with ELK or Seq) can instantly index and filter specific properties (e.g., CustomerId == 5) across millions of entries.

Q15: Rate Limiting and how do it.

• Built-in Middleware: Native rate-limiting middleware configured in Program.cs.

• Core Algorithms: Fixed Window, Sliding Window, Token Bucket, and Concurrency limits.

• app Rule: Set rate-limiting policies globally or target specific routes using [EnableRateLimiting] attribute to defend against DoS attacks.

Q16: Filter Pipelines and execution order of 5 filters?

• Filter Pipelines: Custom code run before or after specific stages in invocation pipeline.

• 1. Authorization Filters: Sees if user is fully verified and authorized for resource.

• 2. Resource Filters: Looks at request and returns cached response.

• 3. Action Filters: Runs right before and immediately after controller action method runs.

• 4. Exception Filters: Handles unhandled controller actions or model binders exceptions.

• 5. Result Filters: Before and after final action result renders.