Google PCA Manage implementation of cloud architecture Practice Question
This PCA practice question tests your understanding of manage implementation of cloud architecture. 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 designing a multi-tier web application on Compute Engine. They need to ensure that only the web tier can access the application tier over a specific port. They plan to use VPC firewall rules. Which approach minimizes the attack surface?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Allow ingress from the web tier's instances' service accounts to the application tier's instances
Option A is correct because it uses service account-based firewall rules, which allow you to specify the source as the service account attached to the web tier's instances rather than their IP addresses or subnets. This ensures that only instances with that specific service account (i.e., the web tier) can reach the application tier on the designated port, regardless of their IP or subnet. By scoping access to a specific identity, you minimize the attack surface because no other instances, even those in the same subnet, can reach the application tier unless they also use that service account.
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.
✓
Allow ingress from the web tier's instances' service accounts to the application tier's instances
Why this is correct
Restricts access based on identity, minimizing attack surface.
Related concept
Read the scenario before looking for a memorised answer.
✗
Allow ingress from any source to the application tier on the port
Why it's wrong here
Allows all traffic, huge attack surface.
✗
Allow ingress from the web tier's subnet to the application tier's instances on the port
Why it's wrong here
Allows all instances in the subnet, still broad.
✗
Allow egress from the web tier to the application tier
Why it's wrong here
Egress rules do not control inbound access to the application tier.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that subnet-based rules are the most secure approach, but the trap here is that service account-based rules provide finer-grained, identity-based access control that reduces the attack surface more effectively than subnet-based rules.
Detailed technical explanation
How to think about this question
GCP VPC firewall rules support service account-based source and target filtering, which is evaluated at the instance level using the instance's attached service account. This allows for identity-aware segmentation that persists even if instances are migrated to different subnets or have dynamic IPs. Under the hood, the firewall rule uses the `--source-service-accounts` flag, and the rule is enforced by the GCP network virtualization layer, which checks the service account of the source instance before allowing the packet. In a real-world scenario, this is critical for compliance frameworks like PCI-DSS that require strict network segmentation based on workload identity rather than IP addresses.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PCA question in full detail.
Manage implementation of cloud architecture — This question tests Manage implementation of cloud architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Allow ingress from the web tier's instances' service accounts to the application tier's instances — Option A is correct because it uses service account-based firewall rules, which allow you to specify the source as the service account attached to the web tier's instances rather than their IP addresses or subnets. This ensures that only instances with that specific service account (i.e., the web tier) can reach the application tier on the designated port, regardless of their IP or subnet. By scoping access to a specific identity, you minimize the attack surface because no other instances, even those in the same subnet, can reach the application tier unless they also use that service account.
What should I do if I get this PCA 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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