The answer is that duplicate CodePipeline executions from S3 event notifications occur because Amazon S3 delivers event notifications on an at-least-once basis, meaning the same object PUT event can be sent multiple times. When CodePipeline uses an S3 bucket as a source, each notification triggers a new pipeline execution, so a single commit can result in two or more runs if S3 duplicates the event. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this question tests your understanding of S3 event notification delivery semantics versus the exactly-once behavior many candidates assume. A common trap is to blame the pipeline configuration or IAM permissions, but the root cause is always the inherent at-least-once design of S3 notifications. To remember this, think of the mnemonic “S3 sends twice, pipeline runs twice” — S3 guarantees delivery, not uniqueness.
DOP-C02 SDLC Automation Practice Question
This DOP-C02 practice question tests your understanding of sdlc automation. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 team uses AWS CodePipeline with a source action from an Amazon S3 bucket. The pipeline triggers on changes to the S3 bucket, but sometimes runs twice for a single commit. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
S3 event notifications for the same object may be delivered more than once.
Amazon S3 event notifications are designed for at-least-once delivery, meaning the same event (e.g., an object PUT) can be delivered multiple times. When CodePipeline uses S3 as a source, it relies on these notifications to trigger the pipeline. If S3 sends duplicate notifications for the same object version, CodePipeline will start a new execution for each notification, causing the pipeline to run twice for a single commit.
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.
✗
CodePipeline has a deduplication setting that is disabled.
Why it's wrong here
CodePipeline does not have a deduplication setting.
✓
S3 event notifications for the same object may be delivered more than once.
Why this is correct
S3 event notifications are at-least-once delivery, so duplicates can occur.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The S3 bucket has versioning enabled.
Why it's wrong here
Versioning does not cause duplicate triggers.
✗
The pipeline is also triggered by a CloudWatch Events rule.
Why it's wrong here
CloudWatch Events would be a separate trigger, but not the most likely cause of duplicates.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume S3 event notifications are exactly-once, leading them to incorrectly suspect versioning or a missing deduplication setting, rather than recognizing S3's inherent at-least-once delivery behavior.
Detailed technical explanation
How to think about this question
S3 event notifications use an at-least-once delivery model, meaning the same event can be sent multiple times due to retries or internal replication. CodePipeline's S3 source action polls for changes or listens for S3 events, but it does not deduplicate identical notifications. In practice, enabling S3 event notification filters (e.g., prefix/suffix) or using S3 EventBridge integration can reduce duplicates, but the fundamental at-least-once guarantee remains.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
SDLC Automation — This question tests SDLC Automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: S3 event notifications for the same object may be delivered more than once. — Amazon S3 event notifications are designed for at-least-once delivery, meaning the same event (e.g., an object PUT) can be delivered multiple times. When CodePipeline uses S3 as a source, it relies on these notifications to trigger the pipeline. If S3 sends duplicate notifications for the same object version, CodePipeline will start a new execution for each notification, causing the pipeline to run twice for a single commit.
What should I do if I get this DOP-C02 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: "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?
Read the scenario before looking for a memorised answer.
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Question Discussion
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