The answer is to use preemptible instances for all nodes and enable automatic restart, as this is the most cost-effective Dataproc cluster design for batch workloads. Preemptible instances cost roughly 80% less than standard instances, making them ideal for fault-tolerant, idempotent batch jobs that can tolerate interruptions. Because these instances can be terminated at any time, enabling automatic restart ensures Dataproc recreates lost nodes without manual intervention, maintaining cluster capacity for the job to complete. On the Google Professional Data Engineer exam, this scenario tests your understanding of cost optimization for transient, resilient workloads—a common trap is choosing a mix of standard and preemptible nodes, which increases cost unnecessarily for a fully fault-tolerant job. Remember the memory tip: “Preempt for price, restart for resilience”—if the job can restart and tolerate failure, go all preemptible with auto-restart to maximize savings.
PDE Designing data processing systems Practice Question
This PDE practice question tests your understanding of designing data processing systems. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company runs a nightly Dataproc batch job to process large log files. The job is idempotent and can tolerate node failures if restarted. Minimizing cost is critical. What is the most cost-effective cluster design?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use preemptible instances for all nodes and enable automatic restart
Preemptible instances cost about 80% less than standard instances, making them the most cost-effective choice for fault-tolerant, idempotent batch jobs. Enabling automatic restart ensures that if a preemptible instance is terminated (which can happen at any time), Dataproc will automatically recreate it, maintaining cluster capacity without manual intervention. This design minimizes cost while preserving the job's ability to complete despite node failures.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 preemptible instances for all nodes and enable automatic restart
Why this is correct
Preemptible instances are 60-80% cheaper, and automatic restart allows the job to continue after a preemption.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use standard instances with autoscaling based on YARN memory
Why it's wrong here
Standard instances are more expensive than preemptible, even with autoscaling.
✗
Use all preemptible instances and configure the cluster to delete after the job completes
Why it's wrong here
Without automatic restart, preemptions can cause the job to fail before completion.
✗
Use a single-node cluster with a high-memory machine type
Why it's wrong here
A single-node cluster may not handle large log files efficiently and can be more expensive per GB of processing.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that deleting the cluster after the job completes is the primary cost-saving measure, but the trap here is that without automatic restart, preemptible instances alone can cause job failure due to node preemption, negating cost benefits.
Detailed technical explanation
How to think about this question
Preemptible instances in Google Cloud are Compute Engine VMs that last up to 24 hours and can be terminated at any time if capacity is needed elsewhere. Dataproc's automatic restart feature leverages the `--enable-component-gateway` and `--num-preemptible-instances` flags to recreate preemptible nodes via the instance group manager, ensuring the cluster remains operational. In practice, for idempotent jobs that can tolerate restarts, this design can reduce costs by up to 80% compared to standard instances, making it ideal for nightly batch processing.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Designing data processing systems — This question tests Designing data processing systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use preemptible instances for all nodes and enable automatic restart — Preemptible instances cost about 80% less than standard instances, making them the most cost-effective choice for fault-tolerant, idempotent batch jobs. Enabling automatic restart ensures that if a preemptible instance is terminated (which can happen at any time), Dataproc will automatically recreate it, maintaining cluster capacity without manual intervention. This design minimizes cost while preserving the job's ability to complete despite node failures.
What should I do if I get this PDE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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