DEA-C01 practice question: Processing with Amazon EMR
Data Ingestion and Transformation A free question from our original DEA-C01 practice exam. Try it, then open the answer to see why each option is right or wrong.
A media analytics company runs a nightly Apache Spark job on an Amazon EMR cluster. The job takes about six hours on the current on-demand instances, and the company wants to cut the cost of the cluster.
The cluster stores intermediate HDFS data on its core nodes during the run. Losing a core node would lose that data and force the job to restart. The company can tolerate an interrupted task, but not a lost core node.
Which configuration meets these requirements?
Choose one answer.
AA. Run the primary, core and task nodes all on Spot Instances, so that the whole cluster costs the least while the job runs.
BB. Keep the primary and core nodes On-Demand and run the task nodes on Spot Instances, so interrupted tasks rerun without losing HDFS data.
CC. Run all nodes On-Demand, and buy Reserved Instances for the cluster's instance types, so that each hour of the nightly run costs less.
DD. Run the primary node on Spot Instances and the core and task nodes On-Demand, so that the cluster's coordinator is the cheapest node to replace.
Show the answer and explanation
Answer: B
A. Wrong: Spot Instances can be reclaimed at any time, and that includes core nodes that hold HDFS data. The company cannot accept losing core nodes, so this option fails the stated constraint.
B. Right: Correct. Task nodes hold no HDFS data, so Spot interruptions only rerun tasks. Keeping the primary and core nodes On-Demand protects HDFS, and the Spot task capacity lowers the overall cost. Learn more: What is Amazon EMR? (opens in a new tab)
C. Wrong: Reserved Instances bill for every hour of their term, but this cluster runs for about six hours a night. The company would pay for reserved capacity that sits unused most of the day, and the option ignores the cheaper Spot capacity that interruptible task nodes can use.
D. Wrong: The primary node coordinates the cluster, and losing it ends the job, so it is a poor candidate for Spot. The option gets the Spot placement backward and does not meet the requirement.
Explanation
EMR cost savings come from Spot Instances on nodes that can be lost safely. Task nodes do not store HDFS data, so Spot reclamation only reruns their work. The primary and core nodes stay On-Demand to protect the cluster's coordination and HDFS data.
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