- A
Delete the message from the queue immediately after receive to prevent redelivery.
Why wrong: Deleting immediately can cause lost work when processing fails after receipt. It doesn’t ensure that retries won’t occur or that state commits are consistent.
- B
Make the payment processing idempotent by recording an idempotency key for each payment and ensuring repeated deliveries do not apply the charge twice.
Idempotency ensures that reprocessing the same payment message has no additional side effects. Recording an idempotency key and using conditional logic prevents duplicate charges.
- C
Increase the queue visibility timeout to a very large value so messages rarely reappear.
Why wrong: A larger visibility timeout reduces redelivery frequency but doesn’t remove duplicates. It can also delay recovery when a consumer crashes or fails permanently.
- D
Switch to a single-threaded consumer with one worker so messages are processed in order.
Why wrong: Single-threaded ordering reduces concurrency issues but doesn’t prevent at-least-once redelivery duplicates. If a timeout occurs, the same message can still be processed again.
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 service processes customer payments from a message queue. Because the queue provides at-least-once delivery, the same payment message can be delivered more than once if the consumer times out before committing its state. Currently, the service sometimes charges the customer twice.
Which design change most directly prevents duplicate charges while still allowing safe retries?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"least"Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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
Make the payment processing idempotent by recording an idempotency key for each payment and ensuring repeated deliveries do not apply the charge twice.
Option B is correct because making payment processing idempotent using an idempotency key ensures that even if the same message is delivered multiple times due to at-least-once delivery semantics, the charge is applied only once. The consumer records a unique key (e.g., payment ID) in a durable store (like DynamoDB or Redis) and checks it before processing; if the key already exists, the charge is skipped. This directly prevents duplicate charges while still allowing safe retries, as the consumer can safely reprocess messages without side effects.
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.
- ✗
Delete the message from the queue immediately after receive to prevent redelivery.
Why it's wrong here
Deleting immediately can cause lost work when processing fails after receipt. It doesn’t ensure that retries won’t occur or that state commits are consistent.
- ✓
Make the payment processing idempotent by recording an idempotency key for each payment and ensuring repeated deliveries do not apply the charge twice.
Why this is correct
Idempotency ensures that reprocessing the same payment message has no additional side effects. Recording an idempotency key and using conditional logic prevents duplicate charges.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the queue visibility timeout to a very large value so messages rarely reappear.
Why it's wrong here
A larger visibility timeout reduces redelivery frequency but doesn’t remove duplicates. It can also delay recovery when a consumer crashes or fails permanently.
- ✗
Switch to a single-threaded consumer with one worker so messages are processed in order.
Why it's wrong here
Single-threaded ordering reduces concurrency issues but doesn’t prevent at-least-once redelivery duplicates. If a timeout occurs, the same message can still be processed again.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse at-least-once delivery with exactly-once delivery and assume that increasing visibility timeouts or using single-threaded consumers will prevent duplicates, when in fact only idempotency guarantees safe retries without duplicate charges.
Detailed technical explanation
How to think about this question
Idempotency keys are commonly implemented using a conditional write to a database (e.g., DynamoDB PutItem with a condition expression on the key attribute) or a Redis SETNX command. If the write succeeds, the payment is processed; if it fails because the key already exists, the charge is skipped. This pattern is essential for distributed systems where network partitions or consumer failures can cause message redelivery, and it aligns with the AWS Well-Architected Framework's recommendation for designing idempotent APIs.
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: Make the payment processing idempotent by recording an idempotency key for each payment and ensuring repeated deliveries do not apply the charge twice. — Option B is correct because making payment processing idempotent using an idempotency key ensures that even if the same message is delivered multiple times due to at-least-once delivery semantics, the charge is applied only once. The consumer records a unique key (e.g., payment ID) in a durable store (like DynamoDB or Redis) and checks it before processing; if the key already exists, the charge is skipped. This directly prevents duplicate charges while still allowing safe retries, as the consumer can safely reprocess messages without side effects.
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: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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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