Interview Q&A

Short answer: Configure CORS policy on the server. Allow specific origins, headers, and methods. 👉 Example in ASP.NET Core: services.AddCors(options => { options.AddPolicy("MyPolicy", builder => builder.WithOrigins(" .AllowAnyHeader() .AllowAnyMethod()); }); Apply with app.UseCors("MyPolicy");.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Idempotent = multiple identical requests have the same effect as one request. Important for reliability and safe retries. HTTP Methods: GET, PUT, DELETE → Idempotent. POST → Not idempotent (creates new resource each time).

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: 2xx Success → 200 (OK), 201 (Created). 4xx Client Errors → 400 (Bad Request), 401 (Unauthorized), 404 (Not Found). 5xx Server Errors → 500 (Internal Server Error), 503 (Service Unavailable). Error responses should include structured messages: { "status": 400, "error": "Invalid Data", "details": "Email is required" }

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Horizontal scaling → Add more servers/containers. Load balancing across multiple instances. Database optimization (indexes, partitioning, read replicas). Caching at server, client, and CDN levels. Use asynchronous processing for long-running tasks. Apply rate limiting and throttling to prevent abuse. Adopt microservices architecture for modular scaling.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use a load balancer (NGINX, HAProxy, AWS ELB, Azure Front Door). Distribute traffic across multiple instances to avoid bottlenecks. Support round-robin, least connections, or IP hash strategies. Enable health checks to route traffic only to healthy instances. Combine with auto-scaling for dynamic traffic management.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Reduce payload size (use JSON instead of XML, compress responses). Implement pagination for large datasets. Apply caching at multiple levels. Use async I/O (non-blocking calls). Minimize database calls (batch queries, stored procedures). Enable GZIP compression on responses. Profile and monitor using APM tools (New Relic, Application Insights).

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Client-side caching → Reduces server calls, but may serve stale data. Server-side caching → Faster responses, but increases memory usage. Proxy caching/CDN → Global scalability, but harder cache invalidation. Database caching (Redis) → Faster queries, but adds complexity and consistency issues.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: REST API? Add query parameters: Filtering: /products?category=shoes&brand=nike Sorting: /products?sort=price_asc Searching: /products?search=wireless+headphones Use LINQ/SQL queries in backend. Ensure query optimization with indexes. Implement validation to prevent SQL injection.

Real-world example (ShopNest)

ShopNest exposes REST APIs for cart and checkout. Controllers stay thin; business rules live in application services.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Add query parameters: Filtering: /products?category=shoes&brand=nike Sorting: /products?sort=price_asc Searching: /products?search=wireless+headphones Use LINQ/SQL queries in backend. Ensure query optimization with indexes. Implement validation to prevent SQL injection.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Deploy servers closer to users (geo-distributed hosting). Use CDNs for static content. Apply connection pooling for databases. Reduce number of API calls (batching, GraphQL alternative). Use HTTP/2 or gRPC for faster communication. Monitor latency with APM tools and optimize bottlenecks.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Swagger/OpenAPI → Standard for REST API design and documentation. Postman → Can generate collections and documentation automatically. Redoc → Static documentation from OpenAPI specs. RAML → RESTful API Modeling Language. Stoplight, Apiary, Docusaurus → Modern documentation and mocking platforms.

Real-world example (ShopNest)

ShopNest exposes REST APIs for cart and checkout. Controllers stay thin; business rules live in application services.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: In ASP.NET Core: Use Swashbuckle package to generate Swagger UI from controllers and annotations.

Explain a bit more

services.AddSwaggerGen(c => { c.SwaggerDoc("v1", new OpenApiInfo { Title = "My API", Version = "v1" }); }); app.UseSwagger(); app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API v1")); Other frameworks (Node.js: swagger-jsdoc, Spring Boot: springdoc-openapi) also support annotations and automatic documentation.

Real-world example (ShopNest)

ShopNest exposes REST APIs for cart and checkout. Controllers stay thin; business rules live in application services.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use try-catch blocks in code to catch exceptions. Implement global exception handling middleware in ASP.NET Core: app.UseExceptionHandler(appError => { appError.Run(async context => {

Example code

context.Response.StatusCode = 500;
context.Response.ContentType = "application/json";
await context.Response.WriteAsync(new { message = "Internal Server Error" }.ToString()); }); }); Log exceptions for debugging and monitoring.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Indicates the requested resource does not exist. Use when resource ID is invalid or missing. Helps clients handle missing data gracefully. Example in ASP.NET Core: var user = db.Users.Find(id);

Example code

if(user == null) return NotFound(new { status=404, error="User not found" });

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use model validation with data annotations: public class UserModel

Example code

{ [Required] [EmailAddress] public string Email { get; set; }
} Return 400 Bad Request with a list of validation errors: { "status": 400, "error": "Validation Failed", "details": ["Email is required", "Password must be at least 6 characters"] }

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: PI? Structured logging with libraries like Serilog, NLog, or built-in ILogger. Log requests and responses, including headers and payloads (avoid sensitive info). Use correlation IDs to trace requests across services. Centralize logs using ELK Stack, Seq, or Azure Application Insights. Log different levels: Information, Warning, Error,… Critical. Example……… using ILogger in ASP.NET Core: private readonly…

Explain a bit more

ILogger<MyController> _logger; public MyController(ILogger<MyController> logger) { _logger = logger; } [HttpGet("{id}")] public IActionResult GetUser(int id) { _logger.LogInformation("Fetching user with id {UserId}", id); try { var user = dbContext.Users.Find(id); if (user == null) { _logger.LogWarning("User with id {UserId} not found", id); return NotFound(); } return Ok(user); } catch (Exception ex) { _logger.LogError(ex, "Error fetching user with id {UserId}", id); return StatusCode(500, "Internal Server Error"); } } This covers all core aspects of error handling and debugging for REST APIs. public MyController(ILogger<MyController> logger)

Example code

{
_logger = logger;
} [HttpGet("{id}")] public IActionResult GetUser(int id)
{ _logger.LogInformation("Fetching user with id {UserId}", id); try {
var user = dbContext.Users.Find(id);
if (user == null)
{ _logger.LogWarning("User with id {UserId} not found", id); return NotFound();
}
return Ok(user);
} catch (Exception ex) { _logger.LogError(ex, "Error fetching user with id {UserId}", id); return StatusCode(500, "Internal Server Error");
}
} This covers all core aspects of error handling and debugging for REST APIs.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Structured logging → Serilog, NLog, or built-in ILogger in ASP.NET Core. Request/response logging for debugging API calls. Correlation IDs to trace requests across microservices. Centralized logging → ELK Stack, Seq, Azure Application Insights. Log errors, warnings, and important info (not sensitive data). Q&A

Example code

Structured logging → Serilog, NLog, or built-in ILogger in ASP.NET Core. Request/response logging for debugging API calls. Correlation IDs to trace requests across microservices. Centralized logging → ELK Stack, Seq, Azure Application Insights. Log errors, warnings, and important info (not sensitive data). Q&A

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.