- A
Pull subscription with exactly-once delivery enabled
Pub/Sub supports exactly-once delivery on pull subscriptions, minimising duplicates while the subscriber processes idempotently.
- B
Push subscription with retry policy
Why wrong: Push subscriptions can have retry policies but do not natively provide exactly-once delivery; they are at-least-once by default.
- C
Push subscription with acknowledgment deadline extended
Why wrong: Extending acknowledgment deadline prevents premature redelivery but does not guarantee exactly-once.
- D
Pull subscription with a dead letter topic
Why wrong: Dead letter topics handle undeliverable messages, not duplicate prevention.
Question 428 of 1,000
Cloud Digital Leader Exactly-once delivery Practice Question
This GCDL practice question tests your understanding of google cloud products and services. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: exactly-once delivery. 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.
An engineer needs to create a Pub/Sub subscription that delivers messages exactly once to a subscriber that processes them idempotently. The subscriber runs on Compute Engine and must handle messages at least once but the engineer wants to minimise duplicates. Which subscription type should be configured?
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
✓
Pull subscription with exactly-once delivery enabled
In Google Cloud Pub/Sub, exactly-once delivery is a property that can be enabled only on pull subscriptions. It ensures that each message is delivered to the subscriber no more than once, reducing duplicates. Push subscriptions do not support exactly-once delivery; they operate on an at-least-once basis. Therefore, the correct configuration is a pull subscription with exactly-once delivery enabled.
Key principle: Exactly-once delivery
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Pull subscription with exactly-once delivery enabled
Why this is correct
Pub/Sub supports exactly-once delivery on pull subscriptions, minimising duplicates while the subscriber processes idempotently.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Exactly-once delivery
- ✗
Push subscription with retry policy
Why it's wrong here
Push subscriptions can have retry policies but do not natively provide exactly-once delivery; they are at-least-once by default.
- ✗
Push subscription with acknowledgment deadline extended
Why it's wrong here
Extending acknowledgment deadline prevents premature redelivery but does not guarantee exactly-once.
- ✗
Pull subscription with a dead letter topic
Why it's wrong here
Dead letter topics handle undeliverable messages, not duplicate prevention.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates may think that push subscriptions also support exactly-once delivery and choose a push option, but the push options listed do not enable exactly-once delivery.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Exactly-once delivery
- Pull subscription
- Idempotent processing
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
Exactly-once delivery
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Review exactly-once delivery, then practise related GCDL questions on the same topic to reinforce the concept.
- →
Google Cloud Products and Services — study guide chapter
Learn the concepts, then practise the questions
- →
Google Cloud Products and Services practice questions
Targeted practice on this topic area only
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All GCDL questions
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Google Cloud Digital Leader study guide
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FAQ
Questions learners often ask
What does this GCDL question test?
Google Cloud Products and Services — This question tests Google Cloud Products and Services — Exactly-once delivery.
What is the correct answer to this question?
The correct answer is: Pull subscription with exactly-once delivery enabled — In Google Cloud Pub/Sub, exactly-once delivery is a property that can be enabled only on pull subscriptions. It ensures that each message is delivered to the subscriber no more than once, reducing duplicates. Push subscriptions do not support exactly-once delivery; they operate on an at-least-once basis. Therefore, the correct configuration is a pull subscription with exactly-once delivery enabled.
What should I do if I get this GCDL question wrong?
Review exactly-once delivery, then practise related GCDL questions on the same topic to reinforce the concept.
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?
Exactly-once delivery
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Last reviewed: Jul 4, 2026
This GCDL practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the GCDL exam.
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