Google PCA Practice Question: Analyze and optimize technical and business processes
An online learning platform runs its API on a regional managed instance group behind an external Application Load Balancer. The operations team wants to release new versions with the ability to shift a small percentage of user traffic to the new version first, then increase it gradually, and roll back instantly if error rates rise. What should they implement?
⚠ Common exam trap
It's easy for candidates to confuse autoscaling or CDN caching with traffic splitting, when only the load balancer's backend weighting controls the share of requests each version receives.
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
✓
Create a second managed instance group for the new version and use the load balancer's backend service with a small weight on the new group.
The Application Load Balancer supports multiple backends per backend service and can distribute traffic by weight or capacity, so registering a second managed instance group for the new version enables a canary. Adjusting weights shifts exposure gradually, and returning the new group's weight to zero restores the previous version immediately.
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 Cloud CDN with a cache key that includes the application version header and purge the cache after each deployment.
Why it's wrong here
Cloud CDN caches responses at edge locations; it does not route a share of users to a new application version. Purging the cache changes what content is served from cache, not which backend version handles a request, so it cannot implement gradual traffic shifting or a controlled rollback.
- ✗
Enable autoscaling on the existing managed instance group and set the target CPU utilization lower during the release window.
Why it's wrong here
Autoscaling changes instance count in response to load; it does not control which version receives traffic. Lowering the CPU target adds capacity but every instance still runs the same template, so users cannot be split between old and new versions and there is no mechanism to shift or revert traffic.
- ✗
Use an internal passthrough Network Load Balancer in front of the managed instance group and switch the target pool during the release.
Why it's wrong here
A passthrough Network Load Balancer operates at layer 4 and balances connections rather than HTTP requests, so it cannot perform percentage-based request routing between versions. Switching target pools is an all-or-nothing cutover, which does not provide gradual exposure or instant rollback based on error rates.
- ✓
Create a second managed instance group for the new version and use the load balancer's backend service with a small weight on the new group.
Why this is correct
Two managed instance groups registered as backends of the same backend service let the Application Load Balancer distribute traffic by capacity or weight, enabling a canary release. Shifting weight gradually controls exposure, and setting the new group's weight back to zero reverts traffic immediately without redeploying, which matches the rollback requirement.
Go deeper
Related to this question
Learn chapter
Cloud SQL and Managed Data Stores
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.
Key term
Service
A service is a software component or system that performs a specific function and is available to be used by other programs or users over a network.
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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.