Google PCA Practice Question: Analysing and Optimising Technical and Business Processes
A company runs a batch processing job that uses preemptible VMs. The job occasionally fails due to VM preemption. They want to improve reliability without significantly increasing cost. Which TWO actions should they take? (Choose TWO.)
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
✓
Use a managed instance group with autoscaling and preemptible VMs
Option A is correct because a managed instance group (MIG) with autoscaling and preemptible VMs automatically maintains the desired number of instances, replacing preempted VMs with new ones so the batch job can continue running with minimal disruption and without paying for non-preemptible capacity. Option D is correct because preemptible VMs can be reclaimed at any time, so building a retry mechanism into the job lets failed tasks be re-run on surviving or replacement instances, directly improving reliability at essentially no extra cost. Option B is not appropriate because sole-tenant nodes isolate hardware for compliance/licensing reasons and do not reduce the risk of preemption. Option C would improve reliability but significantly increases cost, which the scenario explicitly wants to avoid. Option E merely adds more preemptible VMs; it does not address task recovery and still leaves the job vulnerable to preemption.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use a managed instance group with autoscaling and preemptible VMs
Why this is correct
A managed instance group automatically recreates preempted VMs, directly addressing the reliability constraint while retaining preemptible pricing. Autoscaling maintains capacity by adding instances when demand rises, so the batch job recovers without manual intervention. This satisfies the requirement to improve resilience without significantly increasing cost, since preemptible rates still apply.
- ✗
Use sole-tenant nodes to reduce risk of preemption
Why it's wrong here
Sole-tenant nodes only guarantee physical host exclusivity; they do not exempt workloads from preemption, so failures continue. It is tempting because sole-tenant nodes genuinely address compliance and licensing isolation, which is the correct choice when regulatory separation, not preemption resilience, is the requirement.
- ✗
Switch to regular (non-preemptible) VMs
Why it's wrong here
Regular VMs eliminate preemption entirely but bill at full on-demand rates, breaching the requirement to avoid significant cost increases. It is tempting because non-preemptible instances genuinely suit latency-sensitive or stateful workloads, which is the correct choice when reliability outweighs cost.
- ✓
Implement a retry mechanism in the job to re-run failed tasks
Why this is correct
Preemption terminates tasks mid-execution, so a retry mechanism re-runs failed tasks once replacement VMs appear. This directly addresses the intermittent failure mode without changing the compute tier, preserving the cost constraint while improving job completion reliability.
- ✗
Increase the number of preemptible VMs
Why it's wrong here
Adding more preemptible VMs increases parallel capacity but each instance remains reclaimable, so the job still fails when capacity is withdrawn. It is tempting because horizontal scaling genuinely improves throughput for interruption-tolerant work, which is correct when the goal is speed rather than reliability.
Go deeper
Related to this question
Learn chapter
Billing, Budgets, and Cost Management
Key term
Batch processing
Batch processing is a method of running high-volume, repetitive data jobs where a group of transactions is collected, processed together automatically, and then results are produced without real-time user interaction.
Key term
Managed instance group
A managed instance group is a collection of identical virtual machine instances that are automatically managed as a single unit to ensure high availability and scalability.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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