PCD Practice Question: Designing highly scalable, available, and reliable cloud-native applications
This PCD practice question tests your understanding of designing highly scalable, available, and reliable cloud-native applications. 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 developer is building an event-driven system using Cloud Pub/Sub. They need to ensure reliable message delivery and processing. Which three practices should they follow?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use pull subscriptions with synchronous acknowledgment.
Pull subscriptions with synchronous acknowledgment (option B) ensure that a message is not acknowledged until the subscriber has successfully processed it. This prevents premature acknowledgment and message loss, because Cloud Pub/Sub will redeliver the message if the acknowledgment deadline expires without a synchronous ack. This is a core pattern for reliable processing.
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.
✗
Set a minimum number of delivery attempts.
Why it's wrong here
Pub/Sub does not have a minimum; you configure maximum attempts.
✓
Use pull subscriptions with synchronous acknowledgment.
Why this is correct
Sync ack allows you to acknowledge after processing, preventing loss.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use message ordering.
Why it's wrong here
Ordering is not required for reliability; it adds complexity.
✓
Configure a dead-letter topic.
Why this is correct
Dead-letter topics capture messages that fail after retries.
Related concept
Read the scenario before looking for a memorised answer.
✓
Use exponential backoff for pull subscriptions.
Why this is correct
Exponential backoff reduces retry frequency and load on the subscriber.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing reliability features with ordering or delivery attempt counts; Cisco often tests that reliable processing relies on synchronous acknowledgment and dead-letter topics, not on setting a minimum delivery attempts or enabling ordering.
Detailed technical explanation
How to think about this question
Cloud Pub/Sub uses a configurable acknowledgment deadline (default 10 seconds, max 600 seconds) during which the subscriber must acknowledge the message. If the subscriber fails to ack within that window, the message is automatically redelivered. Exponential backoff for pull subscriptions (option E) reduces the rate of pull requests when no messages are available, which lowers API costs and avoids unnecessary load, but it does not directly affect message delivery reliability.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Designing highly scalable, available, and reliable cloud-native applications — This question tests Designing highly scalable, available, and reliable cloud-native applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use pull subscriptions with synchronous acknowledgment. — Pull subscriptions with synchronous acknowledgment (option B) ensure that a message is not acknowledged until the subscriber has successfully processed it. This prevents premature acknowledgment and message loss, because Cloud Pub/Sub will redeliver the message if the acknowledgment deadline expires without a synchronous ack. This is a core pattern for reliable processing.
What should I do if I get this PCD question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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