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 do not require any upfront commitment and provide full control over lifecycle, but they carry the highest hourly price per vCPU. For a job that runs only one hour each night and can be checkpointed, this means paying a premium for the few hours of compute while gaining no benefit from that flexibility — Spot is dramatically cheaper for the same fault-tolerant batch workload. Choosing On-Demand here wastes cost because you are not paying for an entire 24/7 host, yet you still pay the full on-demand rate for those 365 hours per year.

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  Reserved Instances (Standard 1-year)

  Why it's wrong here

  A Standard 1-year Reserved Instance requires you to commit to paying for a fixed instance type in a specific AWS region for the entire year, regardless of actual usage. This job runs only about 365 hours per year, so you would be paying for roughly 8,760 hours while using barely 4% of that capacity; even at a discounted RI rate, the total annual cost exceeds Spot and may even exceed On-Demand when utilization is that low. Reserved Instances are designed for predictable, always-on or steady-state workloads, not a one-hour nightly batch that can be interrupted and resumed.

• ✓

  Spot Instances

  Why this is correct

  Spot Instances let you bid for unused EC2 capacity at discounts of up to 90% compared to On-Demand pricing. AWS can reclaim that capacity with a two-minute interruption notice, but because this batch processing job is checkpointed and resumable, an interruption simply means restarting from the last saved state and continuing toward completion. This makes Spot the most cost-effective option for this workload, especially since the job is inherently fault-tolerant and runs only for short periods.

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  Dedicated Hosts

  Why it's wrong here

  Dedicated Hosts provide a physical server dedicated solely to your use, which is priced per host-hour rather than per instance-hour, making them several times more expensive than On-Demand. They are intended for scenarios like bringing-your-own-license or meeting strict compliance/certification requirements, not for optimizing cost on a short-running batch job. For a workload that runs only one hour nightly, you would be paying for the entire physical host 24/7 while it sits idle the rest of the day, so they are completely inappropriate here.