CSI RESTful API & Middleware Design 3 — Questions and Answers
Question 1: Which middleware pattern stores frequently accessed data closer to the consumer to reduce upstream API calls?
- Circuit breaker
- Caching proxy (Correct answer)
- Load balancer
- Service mesh
Correct answer: Caching proxy
A caching proxy intercepts requests and returns stored responses when valid, reducing latency and backend load.
Question 2: A REST API must expose the same resource in both JSON and XML formats based on client preference. Which mechanism should it use?
- Different URL endpoints for each format
- Query parameter ?format=xml
- HTTP Accept header content negotiation (Correct answer)
- Custom X-Format request header
Correct answer: HTTP Accept header content negotiation
Content negotiation via the Accept header is the HTTP-standard mechanism for clients to specify their preferred response format.
Question 3: What does the Richardson Maturity Model Level 3 (Hypermedia Controls) require of a REST API?
- Use of HTTPS for all endpoints
- Responses that include links guiding clients to available next actions (Correct answer)
- Support for all HTTP verbs on every resource
- JSON as the mandatory response format
Correct answer: Responses that include links guiding clients to available next actions
Level 3 (HATEOAS) requires responses to embed hypermedia links so clients can discover and navigate possible state transitions.
Question 4: In middleware design, a circuit breaker transitions to the 'open' state when:
- Network latency exceeds a threshold once
- A configurable number of consecutive failures occurs (Correct answer)
- The downstream service returns a 200 status
- CPU usage on the middleware host exceeds 80%
Correct answer: A configurable number of consecutive failures occurs
A circuit breaker opens after a defined failure threshold is reached, stopping further calls to the failing downstream service.
Question 5: Which REST API design practice best prevents over-fetching and under-fetching issues?
- Returning full resource representations always
- Implementing GraphQL instead of REST
- Supporting sparse fieldsets via query parameters like ?fields=id,name (Correct answer)
- Versioning every endpoint separately
Correct answer: Supporting sparse fieldsets via query parameters like ?fields=id,name
Sparse fieldsets allow clients to request only the specific fields they need, reducing payload size and avoiding under-fetching.
Question 6: When an API gateway performs request transformation, what is it doing?
- Encrypting the request payload end-to-end
- Modifying request structure or format before forwarding to backend services (Correct answer)
- Authenticating users against an identity provider
- Routing requests based on client geolocation
Correct answer: Modifying request structure or format before forwarding to backend services
Request transformation adapts incoming requests (e.g., headers, body format, parameters) to match what backend services expect.
Question 7: Which HTTP response status code indicates that a REST API resource has been permanently moved to a new URI?
- 302 Found
- 303 See Other
- 301 Moved Permanently (Correct answer)
- 307 Temporary Redirect
Correct answer: 301 Moved Permanently
301 Moved Permanently tells clients and search engines to update their references to the new URI for all future requests.
CSI RESTful API & Middleware Design 3
Which middleware pattern stores frequently accessed data closer to the consumer to reduce upstream API calls?