- A
Ingress rule on frontend: allow tcp:8080 from backend's service account; Egress rule on backend: allow all to internet
Why wrong: Ingress on frontend would allow backend to connect to frontend, which violates the requirement. Also, using service accounts is more complex but not incorrect per se, but the direction is wrong.
- B
Ingress rule on backend: allow tcp:8080 from subnet A; Egress rule on backend: allow all to internet
Correct: Ingress on backend allows frontend-initiated traffic only. Egress on backend allows backend to reach internet for patches. No rule allows backend to initiate to frontend.
- C
Ingress rule on frontend: allow tcp:8080 from subnet B; Egress rule on backend: allow all to internet
Why wrong: Ingress rule on frontend would allow backend to initiate to frontend, which is not allowed. The requirement is backend cannot initiate to frontend.
- D
Ingress rule on backend: allow tcp:8080 from subnet A; Egress rule on frontend: deny all to internet
Why wrong: Egress rule on frontend is not needed. The rule should allow backend to access internet, not frontend.
Quick Answer
The correct answer is an ingress rule on the backend allowing TCP 8080 from subnet A, paired with an egress rule on the backend allowing all traffic to the internet. This works because firewall rules in Google Cloud are stateful and direction-specific: to control firewall rule direction for multi-tier apps, you must think from the perspective of the target instance. The frontend initiates the connection, so the backend needs an ingress rule to accept that inbound traffic; the backend’s outbound patch requests require an egress rule allowing all destinations. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding that ingress rules govern traffic arriving at a resource, while egress rules govern traffic leaving it—a common trap is mistakenly applying an egress rule on the frontend or an ingress rule on the backend for outbound patches. Remember the memory tip: “Ingress for incoming, egress for exiting—always apply the rule on the receiver of the initiation.”
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. 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.
You are designing a multi-tier application with a frontend and backend. The frontend instances are in subnet A (10.0.1.0/24), and the backend instances are in subnet B (10.0.2.0/24). Both subnets are in the same VPC. You want to allow the frontend to communicate with the backend on TCP port 8080, but the backend must not be able to initiate connections to the frontend. Additionally, the backend must be able to send patches to the internet. Which set of firewall rules should you implement?
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
Ingress rule on backend: allow tcp:8080 from subnet A; Egress rule on backend: allow all to internet
Option B is correct because the frontend in subnet A initiates connections to the backend on TCP port 8080, so an ingress rule on the backend allowing traffic from subnet A permits this. An egress rule on the backend allowing all traffic to the internet enables patch downloads. This setup prevents the backend from initiating connections to the frontend, as no egress rule on the backend targets the frontend, and no ingress rule on the frontend allows unsolicited traffic from the backend.
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.
- ✗
Ingress rule on frontend: allow tcp:8080 from backend's service account; Egress rule on backend: allow all to internet
Why it's wrong here
Ingress on frontend would allow backend to connect to frontend, which violates the requirement. Also, using service accounts is more complex but not incorrect per se, but the direction is wrong.
- ✓
Ingress rule on backend: allow tcp:8080 from subnet A; Egress rule on backend: allow all to internet
Why this is correct
Correct: Ingress on backend allows frontend-initiated traffic only. Egress on backend allows backend to reach internet for patches. No rule allows backend to initiate to frontend.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Ingress rule on frontend: allow tcp:8080 from subnet B; Egress rule on backend: allow all to internet
Why it's wrong here
Ingress rule on frontend would allow backend to initiate to frontend, which is not allowed. The requirement is backend cannot initiate to frontend.
- ✗
Ingress rule on backend: allow tcp:8080 from subnet A; Egress rule on frontend: deny all to internet
Why it's wrong here
Egress rule on frontend is not needed. The rule should allow backend to access internet, not frontend.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between ingress and egress rules and the direction of traffic flow; the trap here is that candidates mistakenly place the ingress rule on the frontend (thinking it needs to 'receive' the connection) instead of on the backend, which actually receives the connection from the frontend.
Detailed technical explanation
How to think about this question
In a VPC, firewall rules are stateful by default in many cloud platforms (e.g., AWS, GCP), meaning that if an ingress rule allows a connection, the corresponding return traffic is automatically permitted without an explicit egress rule. However, in this scenario, the requirement is to prevent the backend from initiating connections to the frontend, which is achieved by not allowing any ingress rule on the frontend from the backend and not allowing any egress rule on the backend that targets the frontend. The backend's egress rule to the internet uses a default route (0.0.0.0/0) to reach external patch servers, typically through a NAT gateway or internet gateway.
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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PCSE question test?
Configuring network security — This question tests Configuring network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Ingress rule on backend: allow tcp:8080 from subnet A; Egress rule on backend: allow all to internet — Option B is correct because the frontend in subnet A initiates connections to the backend on TCP port 8080, so an ingress rule on the backend allowing traffic from subnet A permits this. An egress rule on the backend allowing all traffic to the internet enables patch downloads. This setup prevents the backend from initiating connections to the frontend, as no egress rule on the backend targets the frontend, and no ingress rule on the frontend allows unsolicited traffic from the backend.
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.
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 30, 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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