Interview Q&A

rchitecture?

• API Gateway is a single entry point for APIs in a microservices architecture.
• Handles routing, load balancing, authentication, rate limiting, logging,

monitoring.

• Examples: Kong, NGINX, AWS API Gateway, Azure API Management.
• Use when:
• You have multiple microservices.
• Need centralized authentication/security.
• Need rate limiting or monitoring.

• API Gateway is a single entry point for APIs in a microservices architecture.
• Handles routing, load balancing, authentication, rate limiting, logging,

monitoring.

• Examples: Kong, NGINX, AWS API Gateway, Azure API Management.
• Use when:
• You have multiple microservices.
• Need centralized authentication/security.
• Need rate limiting or monitoring.

• 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");.

• Rate limiting restricts the number of API requests per user/IP in a given time.
• Prevents abuse (DDoS, brute force).
• Ensures fair usage and protects backend systems.
• Return 429 Too Many Requests with Retry-After header.

👉 Example: 100 requests/minute per API key.

• Use an API Gateway for routing and orchestration.
• Implement service discovery (Consul, Eureka).
• Use message queues/event buses (RabbitMQ, Kafka) for async communication.
• Apply circuit breakers (Polly in .NET) to handle failures.
• Implement distributed tracing (Jaeger, Zipkin, OpenTelemetry).

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).

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• 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"

}

• Ensures correctness, reliability, performance, and security of APIs.
• Postman → Manual and automated API testing, environment variables, collections.
• Swagger (OpenAPI) → Live documentation, mock servers, auto-generated client

SDKs.

• Automates QA process and reduces bugs in production.

• 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.

• 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.

• 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).

Caching is storing frequently used data temporarily to reduce server load and improve

response time.

Implementation methods:

• HTTP caching headers (Cache-Control, ETag, Expires).
• Reverse proxies (Varnish, NGINX).
• In-memory stores (Redis, Memcached).
• Client-side caching using 304 Not Modified.

• 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.

• Content negotiation allows clients to specify desired response format.
• Uses HTTP headers:
• Accept: application/json → Request JSON.
• Accept: application/xml → Request XML.
• The server returns response in requested format (if supported).

👉 Example in ASP.NET Core: Add XML formatter with

services.AddControllers()

.AddXmlSerializerFormatters();

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.

• 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.

• 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.

PI performance?

• A CDN caches and delivers static or semi-static content from edge servers close to

users.

• Reduces latency and improves response times.
• Helps with traffic offloading, reducing load on origin servers.
• Supports DDoS protection and scaling under heavy loads.

👉 Example: Cloudflare, Akamai, AWS CloudFront.

• A CDN caches and delivers static or semi-static content from edge servers close to

users.

• Reduces latency and improves response times.
• Helps with traffic offloading, reducing load on origin servers.
• Supports DDoS protection and scaling under heavy loads.

👉 Example: Cloudflare, Akamai, AWS CloudFront.

🔹 API Documentation & Tools – Interview Q&A

• 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.

• Swagger/OpenAPI is a specification for defining REST APIs.
• Provides machine-readable and human-readable documentation.
• Enables automatic client SDK generation, testing, and validation.
• Improves team collaboration and consistency in API design.

Answer: Contains all endpoints, request/response formats, parameters, headers, and security details. Acts as a contract between client and server. Used for auto-generating documentation, client SDKs, and mock servers.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• In ASP.NET Core: Use Swashbuckle package to generate Swagger UI from

controllers and annotations.

services.AddSwaggerGen(c =>

{

c.SwaggerDoc("v1", new OpenApiInfo { Title = "My API", Version =

"v1" });

});

pp.UseSwagger();

pp.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json",

"My API v1"));

• Other frameworks (Node.js: swagger-jsdoc, Spring Boot: springdoc-openapi)

lso support annotations and automatic documentation.

• RAML (RESTful API Modeling Language) → YAML-based specification for APIs.
• Focuses on design-first API approach.
• Differences with OpenAPI/Swagger:
• RAML is more design-oriented; Swagger is implementation-oriented.
• OpenAPI has better tooling support and community adoption.

Answer: Postman is a GUI tool for testing REST APIs. Features: Send HTTP requests (GET, POST, PUT, DELETE). Automate tests using Postman Collections. Generate documentation and mock servers. Supports environment variables and CI/CD integration.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.