- A
Assume duplicates never occur because the consumer deletes messages immediately after receiving them.
Why wrong: With SQS at-least-once delivery, duplicates can still occur if processing fails, times out, or crashes before the delete occurs. Even if you delete quickly after receiving, failures after the side effect can still lead to duplicates being delivered later.
- B
Implement idempotent processing using a deduplication key (for example, paymentId) and record completed charges so duplicates are safely ignored.
Idempotency ensures at-most-once side effects even when duplicates are delivered. Persist a record keyed by paymentId (e.g., a unique constraint/conditional write). If the record indicates the payment was already charged, skip the charge for any subsequent duplicate message.
- C
Increase the SQS visibility timeout until duplicates never happen.
Why wrong: Changing visibility timeout only affects when messages are retried. It does not change SQS’s delivery semantics or guarantee that duplicates will never be delivered, nor does it prevent duplicate side effects from being executed.
- D
Use SNS topics instead of SQS so retries are disabled by default.
Why wrong: Switching to SNS does not guarantee exactly-once processing for downstream systems. Duplicate notifications and retries can still occur due to delivery failures and subscriber behavior, so idempotency is still required to enforce at-most-once charging.
SAA-C03 Design Resilient Architectures Practice Question
This SAA-C03 practice question tests your understanding of design resilient architectures. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A system processes events from Amazon SQS and sometimes sees duplicate messages due to retries. The business requirement is that each payment must be charged at most once. What design choice best addresses this resiliency requirement?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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
Implement idempotent processing using a deduplication key (for example, paymentId) and record completed charges so duplicates are safely ignored.
Option B is correct because implementing idempotent processing with a deduplication key (e.g., paymentId) ensures that even if duplicate messages arrive from SQS (due to retries or at-least-once delivery), the consumer can check a record of completed charges and safely ignore duplicates. This satisfies the business requirement of charging each payment at most once without relying on SQS’s best-effort deduplication or message ordering.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Assume duplicates never occur because the consumer deletes messages immediately after receiving them.
Why it's wrong here
With SQS at-least-once delivery, duplicates can still occur if processing fails, times out, or crashes before the delete occurs. Even if you delete quickly after receiving, failures after the side effect can still lead to duplicates being delivered later.
- ✓
Implement idempotent processing using a deduplication key (for example, paymentId) and record completed charges so duplicates are safely ignored.
Why this is correct
Idempotency ensures at-most-once side effects even when duplicates are delivered. Persist a record keyed by paymentId (e.g., a unique constraint/conditional write). If the record indicates the payment was already charged, skip the charge for any subsequent duplicate message.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the SQS visibility timeout until duplicates never happen.
Why it's wrong here
Changing visibility timeout only affects when messages are retried. It does not change SQS’s delivery semantics or guarantee that duplicates will never be delivered, nor does it prevent duplicate side effects from being executed.
- ✗
Use SNS topics instead of SQS so retries are disabled by default.
Why it's wrong here
Switching to SNS does not guarantee exactly-once processing for downstream systems. Duplicate notifications and retries can still occur due to delivery failures and subscriber behavior, so idempotency is still required to enforce at-most-once charging.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume SQS guarantees exactly-once delivery or that increasing visibility timeouts can prevent duplicates, but SQS is designed for at-least-once delivery, and the only reliable way to handle duplicates is to make the consumer idempotent.
Detailed technical explanation
How to think about this question
SQS’s at-least-once delivery guarantee means that a message can be delivered more than once, especially if the consumer fails to delete it within the visibility timeout or if the message is replicated across SQS servers. Idempotency is achieved by storing a deduplication key (e.g., paymentId) in a database with a unique constraint or TTL, so that the first successful charge commits the key, and subsequent duplicates are rejected. This pattern is essential for financial transactions where exactly-once processing is required, and it works even if SQS does not support FIFO queues (which offer exactly-once processing but with lower throughput).
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Resilient Architectures — This question tests Design Resilient Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Implement idempotent processing using a deduplication key (for example, paymentId) and record completed charges so duplicates are safely ignored. — Option B is correct because implementing idempotent processing with a deduplication key (e.g., paymentId) ensures that even if duplicate messages arrive from SQS (due to retries or at-least-once delivery), the consumer can check a record of completed charges and safely ignore duplicates. This satisfies the business requirement of charging each payment at most once without relying on SQS’s best-effort deduplication or message ordering.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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