- A
Enable retry policy on the Pub/Sub subscription to automatically retry failed messages.
Retry policy ensures messages are not lost and are retried until successful.
- B
Batch multiple Pub/Sub messages into a single Cloud Function invocation.
Why wrong: Cloud Functions don't natively batch; using Pub/Sub push subscriptions can send messages one at a time; batching would require custom code.
- C
Configure the Cloud Function with a min instance count and increase max instances.
Min instances reduce cold starts; more max instances handle higher concurrency.
- D
Increase the Cloud Function timeout to the maximum allowed value.
Why wrong: Timeout alone does not address retries; the function may still fail.
- E
Set a longer acknowledgement deadline for the subscription to allow more processing time.
Longer ack deadline reduces the chance of message redelivery due to timeout.
Quick Answer
The answer is to set a longer acknowledgement deadline for the subscription, enable a retry policy on the Pub/Sub subscription, and configure a minimum number of instances for the Cloud Function. These three steps directly address the core challenge of Cloud Pub/Sub reliability with Cloud Functions during peak load: the acknowledgement deadline prevents premature redelivery when processing takes longer, the retry policy ensures failed messages are automatically retried rather than lost, and min instances eliminate cold start latency that compounds retries. On the Google Professional Cloud Developer exam, this scenario tests your understanding of how Pub/Sub’s delivery mechanics interact with serverless scaling—a common trap is to focus only on increasing function timeout or memory, which doesn’t prevent retries from the subscription side. Remember the mnemonic “LAM” for Longer deadline, Automatic retry, and Min instances to keep the three pillars of reliability straight.
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. 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 is building a serverless event-driven application using Cloud Functions and Cloud Pub/Sub. The function processes messages from a Pub/Sub subscription and writes results to Firestore. During peak hours, the function experiences high latency and some messages are being retried multiple times. Which three steps should the team take to improve reliability and scalability? (Choose three.)
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
Enable retry policy on the Pub/Sub subscription to automatically retry failed messages.
Option A is correct because enabling a retry policy on the Pub/Sub subscription ensures that messages that fail to be processed (e.g., due to transient errors or timeouts) are automatically retried. This prevents message loss and improves reliability by allowing the Cloud Function to reprocess messages without manual intervention. The retry policy works with the subscription's acknowledgement deadline, so messages are redelivered if not acknowledged in time.
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.
- ✓
Enable retry policy on the Pub/Sub subscription to automatically retry failed messages.
Why this is correct
Retry policy ensures messages are not lost and are retried until successful.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Batch multiple Pub/Sub messages into a single Cloud Function invocation.
Why it's wrong here
Cloud Functions don't natively batch; using Pub/Sub push subscriptions can send messages one at a time; batching would require custom code.
- ✓
Configure the Cloud Function with a min instance count and increase max instances.
Why this is correct
Min instances reduce cold starts; more max instances handle higher concurrency.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the Cloud Function timeout to the maximum allowed value.
Why it's wrong here
Timeout alone does not address retries; the function may still fail.
- ✓
Set a longer acknowledgement deadline for the subscription to allow more processing time.
Why this is correct
Longer ack deadline reduces the chance of message redelivery due to timeout.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that increasing timeout or batching messages are universal fixes for latency, when in fact serverless scaling and proper acknowledgement handling are the correct levers for reliability and scalability.
Detailed technical explanation
How to think about this question
Under the hood, Pub/Sub uses a pull-based model where the subscriber (Cloud Function) must acknowledge messages within the acknowledgement deadline. If the deadline expires, the message is redelivered. Setting a longer acknowledgement deadline (option E) prevents premature redelivery when processing takes longer, while min/max instances (option C) ensure the function can scale to handle concurrent messages. The retry policy (option A) works with exponential backoff to manage transient failures, reducing the chance of message loss during spikes.
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.
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FAQ
Questions learners often ask
What does this PCD question test?
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: Enable retry policy on the Pub/Sub subscription to automatically retry failed messages. — Option A is correct because enabling a retry policy on the Pub/Sub subscription ensures that messages that fail to be processed (e.g., due to transient errors or timeouts) are automatically retried. This prevents message loss and improves reliability by allowing the Cloud Function to reprocess messages without manual intervention. The retry policy works with the subscription's acknowledgement deadline, so messages are redelivered if not acknowledged in time.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 11, 2026
This PCD 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 PCD exam.
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