An event consumer sometimes processes the same SQS message more than once due to timeouts and retries. The consumer must ensure the payment is not charged twice. What design choice best addresses this requirement?

Assume messages are processed exactly once because SQS uses durable storage.

SQS durability does not imply exactly-once processing. With at-least-once delivery, duplicates can occur due to retries, visibility timeout expiry, or consumer failures.

Increase the consumer visibility timeout to several days so messages are not redelivered.

Long visibility timeouts can reduce redelivery frequency but do not guarantee uniqueness. Failures can still lead to duplicate processing, and very long timeouts delay detection and recovery when errors occur.

Delete the message immediately even if processing fails validation.

Deleting on failure prevents retries and can lose messages that need correction. It can lead to missing payments or inconsistent outcomes rather than preventing duplicates reliably.

What does this SAA-C03 question test?

Read the scenario before looking for a memorised answer.

What is the correct answer to this question?

The correct answer is: Make the payment operation idempotent by using an idempotency key and skipping side effects when the key indicates the payment already succeeded. — Because SQS is at-least-once, duplicate deliveries are expected. The most reliable approach is to make the downstream payment side effect idempotent. Use a deterministic idempotency key (for example, derived from the message’s business transaction identifier) and store the result of processing in durable storage (for example, DynamoDB). Implement logic such that if the key already indicates the payment has been completed, the consumer does not perform the charge again and instead returns successfully. This guarantees correctness even when the same message is processed multiple times. A is wrong because durable storage does not prevent duplicate processing in at-least-once systems. C is wrong because increasing visibility timeout does not provide exactly-once guarantees and can delay remediation. D is wrong because deleting messages on failed validation can cause incorrect business outcomes (missed payments) instead of safely tolerating duplicates.

What should I do if I get this SAA-C03 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.