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.

• ✓

  Spot Instances

  Why this is correct

  Spot Instances are the optimal choice for this batch workload because they offer savings of up to 90% compared to On-Demand pricing, and the EC2 Spot service can reclaim the capacity with only a 2-minute interruption warning. Since the batch processing job runs only 3 hours nightly and is inherently fault-tolerant—it can be paused, checkpointed, and resumed—Spot interruptions are easily handled without significant downtime or data loss. This cost-benefit alignment makes Spot Instances the AWS-recommended purchasing model for non-critical, event-driven, or scheduled batch workloads that tolerate variable availability.

• ✗

  On-Demand Instances

  Why it's wrong here

  On-Demand Instances provide full control with no commitment and the flexibility to run any workload at any time, but they charge a fixed hourly rate per second with no discounts. For a predictable nightly batch job that runs only 3 hours a day, you would still pay the same full price per hour as you would for a server running 24/7, making it drastically more expensive than necessary. Moreover, the batch application is fault-tolerant, so the reliability guarantee of On-Demand (which prevents interruption) is not a requirement, and the premium you pay for that guarantee is wasted.

• ✗

  Reserved Instances

  Why it's wrong here

  Reserved Instances require a 1- or 3-year commitment in exchange for lower hourly rates, which makes sense only for steady-state, always-on workloads that can fully utilize the capacity over the reservation term. This batch application runs for just 3 hours out of a 24-hour day—roughly 12.5% utilization—so a Reserved Instance would idle for 21 hours daily, and your per-hour savings would never offset the cost of paying for the full-time capacity. Even though AWS offers Standard and Convertible RIs, they are not designed for short-duration nightly jobs unless you need guaranteed specific instance families, which this fault-tolerant workload does not, making RIs a poor cost optimization.

• ✗

  Dedicated Instances

  Why it's wrong here

  Dedicated Instances give you physical isolation from other AWS customers by running your instances on dedicated hardware, which can be required for compliance or licensing scenarios, but this isolation comes at a significant premium—often the highest of all purchasing options. Nothing in the stated batch processing requirement calls for physical tenancy; the workload can safely run on shared multi-tenant infrastructure without any impact on performance or security. Choosing Dedicated Instances would unnecessarily inflate compute costs, and unlike Spot, they offer no interruption tolerance or discount for transient workloads, making them the least efficient choice here.

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