SOA-C02 Cost and Performance Optimization Practice Question

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 an On-Demand instance and set up a CloudWatch alarm to stop it when the job completes.

  Why it's wrong here

  An On-Demand instance gives you full control and no interruption, but you pay the full per-hour price for every hour it runs. A CloudWatch alarm that stops the instance after the job completes only prevents idle-hour charges; it does not reduce the compute cost during the actual job execution. Because this batch workload is fault-tolerant and can handle interruptions, On-Demand pricing is unnecessarily expensive compared to Spot capacity.

• ✓

  Use a Spot Instance with a Spot Fleet that includes a fallback to On-Demand if Spot is not available.

  Why this is correct

  A Spot Fleet is the correct choice here because it lets you request Spot Instances at a significantly lower cost while maintaining reliability with an On-Demand fallback. The nightly batch job is fault-tolerant, meaning it can restart or rerun if Spot capacity is reclaimed. If Spot capacity is unavailable or gets interrupted, the Spot Fleet automatically launches an On-Demand instance to ensure the job still completes, giving you a balance of cost savings and capacity assurance.

• ✗

  Use a Dedicated Host to run the job.

  Why it's wrong here

  A Dedicated Host provides a physical server dedicated solely to your use, which is useful for meeting licensing requirements or compliance constraints—but this batch job has no such needs. You pay for the entire host per hour regardless of how many instances you run, so using it for a few hours of nightly work is extremely costly. There is no cost benefit or architectural advantage for a stateless, fault-tolerant batch job, making this option unnecessarily expensive.

• ✗

  Purchase a Reserved Instance for the m5.xlarge instance.

  Why it's wrong here

  Reserved Instances provide a lower hourly rate only in exchange for a 1- or 3-year upfront commitment, and you are billed for every hour of the term—even when the instance is stopped. A nightly batch job that runs for only a few hours would have a very low utilization rate, making the effective cost per running hour far higher than Spot. Since the workload does not require guaranteed capacity and can tolerate interruptions, paying for 24/7 reserved capacity is not cost-effective.

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