SAA-C03 Design Cost-Optimized Architectures Practice Question
A media processing pipeline runs batch jobs on EC2. The jobs can tolerate interruptions because they checkpoint progress to durable storage and can restart. The total workload is variable week-to-week, and there is no need to guarantee capacity at specific times. To reduce compute cost while maintaining correctness, what EC2 purchase option and approach is the best fit?
⚠ Common exam trap
Test-takers frequently choose Reserved Instances or Savings Plans thinking they always provide the best cost savings, but they fail to recognize that Spot Instances are significantly cheaper and perfectly suited for fault-tolerant, checkpointed batch workloads that do not require guaranteed capacity.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use EC2 Spot Instances with interruption handling and restart from checkpoints.
Spot Instances offer up to 90% cost savings compared to On-Demand and are ideal for fault-tolerant, stateless workloads that can checkpoint progress to durable storage. Since the batch jobs can tolerate interruptions and restart from checkpoints, Spot Instances provide the lowest compute cost while maintaining correctness. No other purchase option achieves the same level of cost reduction for this variable, interruption-tolerant workload.
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 EC2 Spot Instances with interruption handling and restart from checkpoints.
Why this is correct
Spot capacity is typically the lowest-cost EC2 option and can be reclaimed by AWS with interruption notices. Because the workload is explicitly restartable and checkpoints to durable storage, interruptions do not break correctness. Since there is no requirement to reserve capacity, the variable workload aligns well with Spot’s spare-capacity model.
- ✗
Use All Upfront Reserved Instances sized for the average weekly workload to minimize cost.
Why it's wrong here
Reserved Instances are commitment-based and are most effective when usage is stable and you can match the commitment scope (instance attributes such as family/region/OS). With week-to-week variability, you risk paying for underutilized commitment capacity. Additionally, Reserved Instances do not provide an interruption model that matches the prompt’s emphasis on interrupt-tolerant execution strategy.
- ✗
Use On-Demand Instances and scale only during business hours to reduce idle time.
Why it's wrong here
On-Demand is more expensive than Spot for interruptible, restartable workloads. Time-based scaling may reduce costs, but it does not take advantage of the largest cost lever available in this scenario: using discounted Spot capacity plus interruption handling.
- ✗
Use Savings Plans with a fixed hourly commitment to ensure capacity for the entire year.
Why it's wrong here
Savings Plans require committing to a steady spend level. A variable week-to-week workload increases the likelihood of underutilizing the commitment (reducing savings or increasing effective cost). Spot better matches a workload where interruptions are acceptable and there is no need for reserved capacity at particular times.
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