Google PCA Ensure solution and operations reliability Practice Question
A retail company runs a customer-facing API on a managed instance group (MIG) of Compute Engine VMs behind an external Application Load Balancer. The SRE team wants the load balancer to stop sending traffic to a VM as soon as the local application health endpoint starts returning HTTP 500, even before the VM is fully unresponsive. Which load balancer component must be configured to achieve this?
⚠ Common exam trap
The trap here is assuming monitoring uptime checks or autoscaling policies steer load balancer traffic, when only the backend service health check actually controls instance rotation.
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 an HTTP health check with a check interval and unhealthy threshold on the backend service, and attach it to the MIG.
For an external Application Load Balancer, the backend service's health check is the mechanism that determines which instances receive traffic. By pointing an HTTP health check at the application's health endpoint, a VM that begins returning HTTP 500 is marked unhealthy once the unhealthy threshold is met and is removed from rotation, so users are not routed to a failing instance while it is still alive.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Set the MIG's autoscaling policy to scale in when CPU utilization drops below a target threshold.
Why it's wrong here
Autoscaling reacts to aggregate resource metrics such as CPU or load balancing capacity, not to application-level error responses. A VM returning HTTP 500 may still show normal CPU, so the autoscaler would not remove it, and scaling decisions apply to group size rather than to which individual instances receive traffic from the load balancer.
- ✗
Enable Cloud CDN on the backend service so that failing responses are cached and served from edge locations.
Why it's wrong here
Cloud CDN caches successful cacheable content at the edge; it does not perform origin health evaluation or remove a failing VM from the load-balancing pool. Caching a 500 response would not stop traffic from reaching the unhealthy VM, and by default error responses are not cached, so it cannot satisfy the requirement to stop sending traffic quickly.
- ✗
Create an uptime check in Cloud Monitoring against the API endpoint and rely on its alerting policy to failover.
Why it's wrong here
Uptime checks observe availability from external probers and generate metrics and alerts, but they are not wired into the Application Load Balancer's traffic-steering path. An alert firing does not remove the VM from the backend, so requests would continue to be routed to the instance returning HTTP 500 until a human or automation intervenes.
- ✓
Configure an HTTP health check with a check interval and unhealthy threshold on the backend service, and attach it to the MIG.
Why this is correct
The backend service's health check is exactly what drives traffic steering for the external Application Load Balancer. Pointing the health check at the application's health endpoint means a VM returning HTTP 500 is marked unhealthy after the unhealthy threshold is reached, so the load balancer drains it from rotation while the VM is still running.
Go deeper
Related to this question
Learn chapter
Google Cloud Compute Options Overview
Key term
Load balancer
A load balancer is a device or software that distributes incoming network traffic across multiple servers so no single server gets overwhelmed.
Key term
Health check
A health check is an automated test that monitors whether a system, application, container, or network service is running correctly and can respond to requests.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Google Cloud exam blueprint
This PCA 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 PCA exam.