SAA-C03 Design Cost-Optimized Architectures Practice Question
A company runs a containerized web application on Amazon ECS with a steady baseline of 10 tasks that must run continuously. During business hours, traffic spikes require up to 30 additional tasks that can be terminated at any time. The company wants to minimize costs while ensuring the baseline tasks are always available. Which combination of purchasing options should be used for the ECS tasks?
⚠ Common exam trap
The trap here is using Spot Instances for the baseline tasks, which could be interrupted and violate the availability requirement, or using On-Demand for the baseline and missing the savings from Reserved Instances or Savings Plans.
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 Reserved Instances or Savings Plans for the baseline and Spot Instances for the additional tasks.
The baseline of 10 tasks runs continuously, so Reserved Instances or Savings Plans offer the best discount for that predictable usage. The additional tasks are variable and can be interrupted, making Spot Instances ideal for cost savings. Combining these two purchasing options aligns cost with the characteristics of each workload component, ensuring availability for the baseline while minimizing spend on the spikes.
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 Dedicated Hosts for the baseline and On-Demand Instances for the additional tasks.
Why it's wrong here
Dedicated Hosts are expensive and typically used for licensing or compliance, not cost optimization. On-Demand Instances for the additional tasks are also more costly than Spot. This combination would result in much higher costs than necessary and does not leverage the cost benefits of Reserved Instances or Spot for the respective workloads.
- ✗
Use On-Demand Instances for the baseline and Spot Instances for the additional tasks.
Why it's wrong here
On-Demand Instances for the baseline provide availability but are more expensive than Reserved Instances for steady-state usage. While Spot Instances for the additional tasks are cost-effective, the baseline could be covered by Reserved Instances or Savings Plans for further savings. This option does not fully minimize costs for the predictable baseline.
- ✓
Use Reserved Instances or Savings Plans for the baseline and Spot Instances for the additional tasks.
Why this is correct
Reserved Instances or Savings Plans provide significant discounts for the steady baseline of 10 tasks, ensuring predictable capacity and cost. Spot Instances handle the variable additional tasks at up to 90% discount, and their interruptible nature is acceptable for the spike capacity. This combination minimizes cost while maintaining baseline availability.
- ✗
Use Spot Instances for all tasks, including the baseline, to maximize savings.
Why it's wrong here
Spot Instances can be interrupted, so using them for the baseline tasks risks terminating essential capacity. The requirement states the baseline must always be available, which Spot cannot guarantee. This approach may save money but fails the availability requirement for the baseline tasks, making it unsuitable.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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