In MDC3 API design, idempotency is particularly important in which scenario?

• A. When a request is a one-time admin task.
• B. When the operation is a read-only query.
• C. When data must be encrypted in transit.
• D. When a client retries a failed request, such as a create operation.

Answer: (D)

Idempotency is about making repeated identical requests have the same effect as a single one. In MDC3 API design, this matters most when a client might retry after a failure, such as a failed create operation. If the create is not idempotent, a retry can unintentionally create multiple resources or perform the same action multiple times, leading to duplicates and inconsistent state. By designing the API to be idempotent for retries—often by using an idempotency key provided by the client or by upserting the resource on repeated requests—the first successful result is reused for any subsequent identical retries, ensuring safe recovery from transient errors. Read-only queries don’t change state, so retries don’t risk duplication in the same way, and encryption or non-retryable admin tasks aren’t the scenario that most highlights the need for idempotency.