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.

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  On-Demand Instances

  Why it's wrong here

  On-Demand Instances let you run EC2 capacity with no upfront commitment and per-second billing, which sounds flexible for a nightly 2-hour batch. However, you pay the full On-Demand price for every hour the instances run, with no discount for the predictable schedule or for the workload's ability to survive interruptions. Since the batch is interruption-tolerant and runs only briefly each night, paying this premium for guaranteed continuous availability is wasteful; Spot Instances offer the same compute at a fraction of the cost.

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  Reserved Instances

  Why it's wrong here

  Reserved Instances provide a discount for a 1- or 3-year commitment, which is not cost-effective for a workload that runs only 2 hours per night. The upfront commitment does not align with the usage pattern.

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  Spot Instances

  Why this is correct

  Spot Instances operate using spare EC2 capacity that AWS makes available at a significantly reduced hourly rate—often up to 90% off On-Demand pricing. This is the best fit here because the nightly 2-hour batch is both short and fault-tolerant: if capacity is reclaimed, work can be re-queued or resumed without violating the batch window. You can further reduce interruption risk by using a Spot Fleet with multiple instance types and by implementing checkpointing so progress is saved between runs. The result is a dramatic cost reduction for a workload that would otherwise be idling and paying full price.

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  Dedicated Hosts

  Why it's wrong here

  Dedicated Hosts provide you with a physical EC2 server that is exclusively yours, enabling you to bring your own server-bound licenses (for example, Windows Server or SQL Server) and meet strict compliance requirements. You are charged for the host itself per hour, not per instance, and the cost is incurred 24/7 regardless of whether the host is running your nightly batch or sitting idle. For a workload that runs only two hours per night, this is the least cost-effective choice—you pay for the entire host while using it only a fraction of the time, and you lose the per-second billing flexibility that On-Demand or Spot offers.