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 to ensure the job runs every night.

  Why it's wrong here

  Using On-Demand Instances guarantees the job will run every night because AWS never reclaims them, but you pay the full per-second price with no discount. A batch job that runs only a few hours per night spends most of the billing cycle idle, so the hourly cost makes this the least economical option. For a fault-tolerant workload that can tolerate interruptions, On-Demand forfeits the 50–90% savings Spot Instances offer without providing any reliability benefit beyond what a well-designed Spot strategy can achieve.

• ✗

  Purchase a Reserved Instance for 1 year to get a discount.

  Why it's wrong here

  Reserved Instances require a 1- or 3-year commitment and bill you at a discounted hourly rate for every hour of the term, whether the instance is running or not. A nightly batch job that runs only a few hours each day would pay for 24 hours of reserved capacity while using it only a fraction of that time, making the effective cost per executed job very high. RIs are cost-effective for steady-state, always-on workloads, not for short, intermittent jobs that could simply be launched and terminated on demand.

• ✗

  Launch a Dedicated Host to ensure consistent performance.

  Why it's wrong here

  A Dedicated Host provides a physical server solely for your use, which is useful for licensing or compliance requirements, but you are billed for the entire host every hour regardless of how many instances you run. It is the most expensive EC2 pricing model and offers no performance advantage for a batch job that depends only on vCPUs and memory, not on hardware isolation. Launching a dedicated host for a few hours of nightly processing wastes money and does not make the job any more reliable than using regular instances in the same highly available AWS environment.

• ✓

  Use a Spot Instance that can be interrupted but is significantly cheaper.

  Why this is correct

  Spot Instances are the correct choice because they offer significant cost savings, up to 90% off On-Demand pricing, in exchange for the possibility of interruption with a two-minute warning. A batch processing job is typically fault-tolerant and can be designed to checkpoint progress or be reprocessed from the last saved state, making it an ideal Spot workload. Even if Spot capacity is reclaimed, you can automatically relaunch the instance or use AWS Batch to retry the job, so the job still completes every night at a fraction of the cost.

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