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. Users report intermittent 503 errors during traffic spikes. Which action should the company take to improve reliability?
⚠ Common exam trap
Google Cloud often tests the misconception that scaling-related errors are always solved by increasing capacity or adjusting scaling parameters, when in fact the root cause is often a misconfigured health check or insufficient initialization time for new instances.
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 a health check with a sufficient initial delay (grace period) in the MIG
Intermittent 503 errors during traffic spikes often indicate that new VM instances are being started but are not yet ready to serve traffic, causing the load balancer to forward requests to them prematurely. Configuring a health check with a sufficient initial delay (grace period) in the MIG ensures that newly created instances are given time to fully initialize and pass health checks before they receive traffic, preventing 503 errors. This directly addresses the root cause by allowing the application to become healthy before being added to the load balancer's backend.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Change the load balancer from regional to global
Why it's wrong here
A global load balancer changes the traffic entry point, not the capacity of the MIG behind it; 503s during spikes stem from backend exhaustion or health-check failures. Global load balancing suits multi-region failover and latency-based routing, not scaling a single regional MIG.
- ✓
Configure a health check with a sufficient initial delay (grace period) in the MIG
Why this is correct
During autoscaling spikes, new instances need time to boot before serving. A health check with a sufficient initial delay prevents the MIG from marking them unhealthy and removing them prematurely, eliminating the 503 errors caused by premature traffic routing.
- ✗
Increase the autoscaling cool-down period from 60s to 120s
Why it's wrong here
Lengthening the cool-down delays adding capacity after a scale-out trigger, so instances arrive later and 503s persist during spikes. It is tempting because cool-down prevents thrashing, but that tuning suits stable, predictable load rather than bursty traffic needing rapid scale-out.
- ✗
Increase the maximum number of instances in the MIG
Why it's wrong here
Raising the maximum instance count only helps if autoscaling actually reaches that ceiling; the 503s indicate capacity is not being added fast enough, which the ceiling does not address. It is tempting because it removes an upper bound, but that suits sustained growth, not spike latency.
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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