The answer is a transient cluster with a mix of on-demand and spot instances, terminated after the job completes. This configuration is most cost-effective because spot instances can reduce compute costs by up to 90% for fault-tolerant Spark workloads, and a transient cluster automatically shuts down when the batch finishes, eliminating idle charges. The hourly batch arrival and 4-hour processing window make this ideal for leveraging spot instance interruptions, as Spark’s built-in resilience can recover lost tasks on remaining nodes. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of cost optimization for predictable, large-scale ETL pipelines—a common trap is choosing EMR Serverless, which can be pricier for steady, high-volume workloads, or selecting a single large instance, which reduces parallelism and increases runtime. Memory tip: think “transient + spot = transient spot savings” for any batch Spark job with a defined completion window.
MLS-C01 Data Engineering Practice Question
This MLS-C01 practice question tests your understanding of data engineering. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 data engineering team is building a pipeline to process terabytes of log data daily using Amazon EMR with Spark. The data arrives in hourly batches and must be processed within 4 hours. The team needs to minimize cost. Which cluster configuration is MOST cost-effective?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a transient cluster with a mix of on-demand and spot instances, terminated after the job completes.
Option B is correct because spot instances offer significant cost savings and are suitable for fault-tolerant Spark jobs. Option A is wrong because on-demand is more expensive. Option C is wrong because a single large instance reduces parallelism. Option D is wrong because EMR Serverless may be more expensive for predictable, large workloads.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 single large instance with multiple cores to avoid data shuffling.
Why it's wrong here
Single instance limits parallelism and increases runtime.
✓
Use a transient cluster with a mix of on-demand and spot instances, terminated after the job completes.
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Use a long-running cluster of on-demand instances to avoid startup time.
Why it's wrong here
Long-running clusters incur cost even when idle.
✗
Use Amazon EMR Serverless to automatically scale.
Why it's wrong here
EMR Serverless may be less cost-effective for large, predictable workloads.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related MLS-C01 NAT questions on configuration and troubleshooting.
Data Engineering — This question tests Data Engineering — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use a transient cluster with a mix of on-demand and spot instances, terminated after the job completes. — Option B is correct because spot instances offer significant cost savings and are suitable for fault-tolerant Spark jobs. Option A is wrong because on-demand is more expensive. Option C is wrong because a single large instance reduces parallelism. Option D is wrong because EMR Serverless may be more expensive for predictable, large workloads.
What should I do if I get this MLS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related MLS-C01 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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