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200-901 Practice Question: An application developer is designing a…
An application developer is designing a microservice that communicates over HTTP. The service must guarantee that the request is processed exactly once. Which HTTP method should be used to ensure idempotency?
⚠ Common exam trap
Cisco often tests the misconception that POST can be made idempotent with client-side logic, but the question explicitly asks for an HTTP method that ensures idempotency by design, and POST is inherently non-idempotent per the HTTP specification.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
PUT
PUT is idempotent, meaning multiple identical requests produce the same result as a single request, which guarantees that the request is processed exactly once. In HTTP, idempotency ensures that if a client sends the same PUT request multiple times (e.g., due to network retries), the server state remains consistent. This is defined in RFC 7231, where PUT is explicitly listed as an idempotent method, making it suitable for the requirement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
PUT
Why this is correct
PUT is idempotent; repeating the request yields the same result.
- ✗
PATCH
Why it's wrong here
PATCH is not guaranteed to be idempotent.
- ✗
GET
Why it's wrong here
GET is idempotent but not suitable for submitting data.
- ✗
DELETE
Why it's wrong here
DELETE is idempotent but not for request processing.
- ✗
POST
Why it's wrong here
POST is not idempotent; duplicate requests may cause multiple creations.
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