Google PCA Ensure solution and operations reliability Practice Question
A company runs a critical application on Compute Engine instances in a managed instance group (MIG) with autoscaling. During a traffic spike, some instances become unhealthy but are not automatically replaced. What is the most likely cause?
⚠ Common exam trap
Google Cloud often tests the distinction between the MIG's autohealing health check and the load balancer's health check, leading candidates to incorrectly attribute instance replacement failures to load balancer issues rather than the MIG's own health check configuration.
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
✓
The autohealing health check is misconfigured.
The most likely cause is that the autohealing health check is misconfigured. In a managed instance group, autohealing relies on a health check to detect unhealthy instances and trigger replacement. If the health check is misconfigured (e.g., wrong port, path, or protocol), the MIG will not recognize instances as unhealthy and will not automatically replace them, even during a traffic spike.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The MIG is regional and one zone failed.
Why it's wrong here
Regional MIGs automatically redistribute instances across zones; a single zone failure would cause instance recreation in other zones.
- ✓
The autohealing health check is misconfigured.
Why this is correct
MIG autohealing relies on a health check to detect unhealthy instances and replace them; a misconfiguration prevents detection.
- ✗
The instance template has a startup script error.
Why it's wrong here
A startup script error would cause instances to never become healthy but would not prevent replacement of already unhealthy instances.
- ✗
The HTTP load balancer's health check is failing.
Why it's wrong here
The load balancer health check determines traffic routing, not instance replacement by the MIG.
Go deeper
Related to this question
Learn chapter
Google Cloud Compute Options Overview
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.
Key term
Instance group
An instance group is a collection of virtual machine instances that are managed as a single unit for scaling, load balancing, and lifecycle management in cloud computing.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.