The answer is a Lambda function timeout combined with an SQS visibility timeout set to 20 minutes. This is the most likely cause because the Lambda function has a default 30-second timeout, and when it fails to complete processing within that window, the function errors out. The SQS queue then makes the message visible again after the visibility timeout expires, causing the exact same message to be retried every 20 minutes, which explains the perfectly spaced error pattern at 00:10, 00:30, and 00:50. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how Lambda timeouts interact with SQS redrive mechanics, often appearing as a trap where candidates mistakenly blame throttling or memory issues. The key insight is that the regular 20-minute interval directly matches the visibility timeout, not a random retry delay. Remember the mnemonic: “Time out, then retry—match the interval to the visibility sky.”
SAP-C02 Continuous Improvement for Existing Solutions Practice Question
This SAP-C02 practice question tests your understanding of continuous improvement for existing solutions. 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.
Network Topology
A solutions architect sees the above CloudWatch metric data for a Lambda function. The function is triggered by an SQS queue. The errors occur in a pattern: exactly 5 errors at 00:10, 00:30, and 00:50. What is the MOST likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Why wrong: Would cause out-of-memory errors, not timeouts.
B
The Lambda function is timing out due to long-running processing, and the SQS visibility timeout is set to 20 minutes, causing the same messages to be retried.
The pattern matches a timeout and retry cycle.
C
The Lambda function is hitting the reserved concurrency limit.
Why wrong: Would cause throttling, not errors.
D
The Lambda function is using an incompatible runtime.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Lambda function is timing out due to long-running processing, and the SQS visibility timeout is set to 20 minutes, causing the same messages to be retried.
Option A is correct because the pattern suggests the function times out after 30 seconds of processing, and the SQS messages become visible again after the visibility timeout. The errors at regular intervals (20 minutes) indicate that the function retries the same messages. Option B is wrong because insufficient concurrency would cause throttles, not errors. C is wrong because memory would cause out-of-memory errors, not timeouts. D is wrong because runtime updates would cause all invocations to fail.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The Lambda function is running out of memory.
Why it's wrong here
Would cause out-of-memory errors, not timeouts.
✓
The Lambda function is timing out due to long-running processing, and the SQS visibility timeout is set to 20 minutes, causing the same messages to be retried.
Why this is correct
The pattern matches a timeout and retry cycle.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The Lambda function is hitting the reserved concurrency limit.
Why it's wrong here
Would cause throttling, not errors.
✗
The Lambda function is using an incompatible runtime.
Why it's wrong here
Would cause all invocations to fail.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SAP-C02 NAT questions on configuration and troubleshooting.
Continuous Improvement for Existing Solutions — This question tests Continuous Improvement for Existing Solutions — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The Lambda function is timing out due to long-running processing, and the SQS visibility timeout is set to 20 minutes, causing the same messages to be retried. — Option A is correct because the pattern suggests the function times out after 30 seconds of processing, and the SQS messages become visible again after the visibility timeout. The errors at regular intervals (20 minutes) indicate that the function retries the same messages. Option B is wrong because insufficient concurrency would cause throttles, not errors. C is wrong because memory would cause out-of-memory errors, not timeouts. D is wrong because runtime updates would cause all invocations to fail.
What should I do if I get this SAP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SAP-C02 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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