- A
Use VPC Service Controls to restrict access to the database instances.
Why wrong: VPC Service Controls are for accessing Google-managed services, not for Compute Engine instances.
- B
Remove the firewall rule allowing all traffic from the public subnet to the private subnet, and rely on the default allow internal rule.
Why wrong: The default allow internal rule only applies to the same VPC and subnet, not across subnets.
- C
Change the existing rule to allow traffic only on ports 3306 and 443 from the public subnet to the private subnet.
Why wrong: Allowing port 443 from the public subnet to the private subnet is unnecessary and still too permissive.
- D
Create a new firewall rule that allows TCP traffic on port 3306 (MySQL) from the web servers' service accounts to the database servers' IP ranges.
This restricts traffic to only the necessary port and source, meeting PCI DSS requirement.
Quick Answer
The correct solution is to create a new firewall rule that allows TCP traffic on port 3306 (MySQL) from the web servers’ service accounts to the database servers’ IP ranges. This directly implements PCI DSS network segmentation firewall rules least privilege by replacing the overly permissive “allow all” rule with a precise filter that restricts traffic to only the necessary protocol and port, using service accounts as the source identity rather than an entire subnet. On the Google Professional Cloud Security Engineer exam, this scenario tests your ability to apply identity-aware firewall rules for compliance, a common trap being the temptation to simply narrow the source IP range instead of leveraging service accounts for granular control. The key insight is that PCI DSS requirement 1.3.2 demands least privilege at both the network and identity layers, so specifying the web servers’ service accounts ensures only authorized instances can initiate database connections. Memory tip: think “service account, not subnet” to lock down east-west traffic.
PCSE Supporting compliance requirements Practice Question
This PCSE practice question tests your understanding of supporting compliance requirements. 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. 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 company has a single Google Cloud project with multiple VPC networks. They need to comply with PCI DSS requirement 1.3.2, which restricts inbound and outbound traffic to only what is necessary. They have a web application running on Compute Engine instances in a VPC with a public subnet and a private subnet. The web servers in the public subnet need to communicate with database servers in the private subnet. Currently, the security engineer has configured firewall rules to allow HTTP/HTTPS traffic from the internet to the web servers, and allow all traffic from the public subnet to the private subnet. The auditor flags that the rule allowing all traffic from the public subnet to the private subnet is too permissive. What should the security engineer do to meet the requirement while maintaining functionality?
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
Create a new firewall rule that allows TCP traffic on port 3306 (MySQL) from the web servers' service accounts to the database servers' IP ranges.
Option D is correct because it implements a least-privilege firewall rule that restricts traffic to only the necessary MySQL port (3306) and uses service accounts as the source identity, which aligns with PCI DSS requirement 1.3.2. By specifying the web servers' service accounts as the source and the database servers' IP ranges as the destination, the rule ensures only authorized web server instances can initiate database connections, rather than allowing all traffic from the entire public subnet. This maintains the required functionality while eliminating the overly permissive 'allow all' rule.
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.
- ✗
Use VPC Service Controls to restrict access to the database instances.
Why it's wrong here
VPC Service Controls are for accessing Google-managed services, not for Compute Engine instances.
- ✗
Remove the firewall rule allowing all traffic from the public subnet to the private subnet, and rely on the default allow internal rule.
Why it's wrong here
The default allow internal rule only applies to the same VPC and subnet, not across subnets.
- ✗
Change the existing rule to allow traffic only on ports 3306 and 443 from the public subnet to the private subnet.
Why it's wrong here
Allowing port 443 from the public subnet to the private subnet is unnecessary and still too permissive.
- ✓
Create a new firewall rule that allows TCP traffic on port 3306 (MySQL) from the web servers' service accounts to the database servers' IP ranges.
Why this is correct
This restricts traffic to only the necessary port and source, meeting PCI DSS requirement.
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 that candidates often assume VPC Service Controls (Option A) can restrict instance-to-instance traffic, or they mistakenly think the default allow internal rule (Option B) is subnet-specific, when in reality it applies to all instances in the VPC, and they may also overlook that allowing HTTPS (port 443) to database servers (Option C) is unnecessary and violates least privilege.
Detailed technical explanation
How to think about this question
In Google Cloud VPC, firewall rules are stateful and can use service accounts as source or destination targets, enabling granular identity-based access control beyond IP ranges. When a rule specifies a service account as the source, only instances with that service account attached can match the rule, which is critical in dynamic environments where instance IPs may change due to auto-scaling or rolling updates. This approach also simplifies compliance audits by tying network permissions to workload identities rather than static 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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
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FAQ
Questions learners often ask
What does this PCSE question test?
Supporting compliance requirements — This question tests Supporting compliance requirements — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a new firewall rule that allows TCP traffic on port 3306 (MySQL) from the web servers' service accounts to the database servers' IP ranges. — Option D is correct because it implements a least-privilege firewall rule that restricts traffic to only the necessary MySQL port (3306) and uses service accounts as the source identity, which aligns with PCI DSS requirement 1.3.2. By specifying the web servers' service accounts as the source and the database servers' IP ranges as the destination, the rule ensures only authorized web server instances can initiate database connections, rather than allowing all traffic from the entire public subnet. This maintains the required functionality while eliminating the overly permissive 'allow all' rule.
What should I do if I get this PCSE 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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Last reviewed: Jun 11, 2026
This PCSE 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 PCSE exam.
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