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PCSE Practice Question: Your company is deploying a web application on…
Your company is deploying a web application on Google Kubernetes Engine (GKE) with an Internal Load Balancer (ILB) as the ingress. The application must only be accessible from within the same VPC and from an on-premises network connected via Cloud VPN. The on-premises network uses IP range 10.0.0.0/8. You have already created the ILB with a backend service. What is the most secure way to restrict access to the ILB?
⚠ Common exam trap
Google Cloud often tests the misconception that VPC firewall rules can be applied to a load balancer's forwarding rule IP address, but in reality, firewall rules only apply to VM instances or GKE nodes, not to forwarding rules or load balancer IPs.
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
✓
Configure the backend service's firewall rules to only allow traffic from the ILB's health check ranges and from the VPC and on-premises source ranges
The most secure way to restrict access to an Internal Load Balancer (ILB) is to apply firewall rules directly on the backend service (the instance group or NEG). This ensures that only traffic from the ILB's health check probe ranges (130.211.0.0/22 and 35.191.0.0/16 for GKE) and the allowed source ranges (VPC and on-premises) can reach the backend instances. This approach prevents any traffic from reaching the backend except through the ILB, which is the intended secure design for an internal-only application.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure a VPC firewall rule to deny all ingress traffic to the ILB's forwarding rule IP address, and then create a higher-priority allow rule for the VPC and on-premises ranges
Why it's wrong here
Firewall rules apply to instances, not to forwarding rules directly. ILB traffic passes through firewall rules applied to the backend instances, but the ILB itself is not subject to firewall rules.
- ✓
Configure the backend service's firewall rules to only allow traffic from the ILB's health check ranges and from the VPC and on-premises source ranges
Why this is correct
Correct: Firewall rules on the backend instances allow traffic from the ILB's health check probes and from permitted source ranges, ensuring only desired traffic reaches the application.
- ✗
Use GKE Network Policy to restrict ingress traffic to the application pods from the VPC and on-premises ranges
Why it's wrong here
GKE Network Policy controls pod-to-pod traffic but does not restrict traffic entering the cluster through the ILB, which arrives at the node and is then routed to the pod.
- ✗
Use Cloud Armor to create a security policy that allows traffic only from the VPC and on-premises ranges, and attach it to the ILB
Why it's wrong here
Cloud Armor is not supported for Internal Load Balancers; it only works with external load balancers.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.