SAA-C03 Design Cost-Optimized Architectures Practice Question
A media company runs a 24/7 recommendation engine on EC2 in one AWS Region. The workload is interruption-intolerant, and the team expects steady usage but may change instance families and sizes during planned optimizations. Compared to the current On-Demand setup, they want the lowest cost while avoiding the rigidity of locking to a specific instance type.
What should the solutions architect recommend?
⚠ Common exam trap
Watch out — candidates often choose Spot Instances for cost savings without considering the interruption-intolerant requirement, or they select Standard Reserved Instances for the highest discount without recognizing the rigidity penalty for planned instance family changes.
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
✓
Purchase a Compute Savings Plan for the expected steady hourly usage in that Region.
B is correct because a Compute Savings Plan offers the lowest cost for steady-state workloads without locking to a specific instance type, providing up to 66% discount compared to On-Demand while allowing flexibility to change instance families, sizes, OS, or tenancy within a Region. This matches the requirement for cost savings and flexibility during planned optimizations.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Switch the instances to Spot Instances and use interruption handling because it is the largest discount.
Why it's wrong here
Spot Instances offer steep discounts (often up to 90%) but EC2 can reclaim them with only a two-minute warning when capacity is needed elsewhere, making them unsuitable for an interruption-intolerant service like a 24/7 recommendation engine that must deliver results continuously. Even with sophisticated interruption handling (checkpointing, diversified instance pools), you still face the risk of losing capacity, which breaks the workload's availability guarantees. In short, the largest discount is worthless if the workload cannot tolerate interruptions, which is why the correct answer is a Compute Savings Plan that combines significant savings with reliable capacity.
When this WOULD be correct
A question where the workload is fault-tolerant, can handle interruptions (e.g., batch processing, data analysis), and cost reduction is the top priority, with no requirement for steady, uninterruptible compute.
- ✓
Purchase a Compute Savings Plan for the expected steady hourly usage in that Region.
Why this is correct
Compute Savings Plans offer lower hourly rates in exchange for a 1- or 3-year commitment, but the discount applies to any EC2 instance family/type/size in the chosen Region (even Fargate/Lambda). Because the recommendation engine runs 24/7, committing to the expected steady hourly usage captures the discount while preserving the ability to change instance families or sizes as needs evolve. Unlike Standard RIs, you're not locked into a specific instance type, so you get both cost savings and operational flexibility.
- ✗
Purchase a Standard Reserved Instance tied to a single specific instance type for the next 3 years.
Why it's wrong here
A Standard Reserved Instance locks you to a specific instance family and size (e.g., m5.large) for a 1- or 3-year term, and any change to a different instance type requires a modification or exchange that may not fully preserve the discount. For a media recommendation engine that might need to adopt newer instance families with better ML acceleration or newer CPU generations, this rigidity often results in overpaying or running a mismatched fleet. Compute Savings Plans cover the same steady hourly usage but allow the flexibility to change instance types without losing the commitment benefit.
When this WOULD be correct
A company has a predictable, steady-state workload that uses a specific instance type for 1-3 years, with no plans to change instance families or sizes, and seeks the maximum discount over On-Demand.
- ✗
Keep On-Demand and rely on Auto Scaling to reduce capacity when utilization is low.
Why it's wrong here
Auto Scaling with On-Demand instances adjusts capacity to match demand, but the workload in question runs 24/7 with steady utilization, meaning the baseline capacity must stay constantly active and incurs On-Demand rates every hour. Auto Scaling can shave off unused capacity during occasional lulls, but it cannot lower the per-hour price paid for the predictable baseline, so the total compute cost remains far higher than any commitment-based option. The best practice is to pair Auto Scaling with a Savings Plan, not to rely on Auto Scaling alone as the primary cost-control mechanism.
When this WOULD be correct
A company has a variable workload that experiences predictable low-usage periods (e.g., nightly or seasonal drops) and can tolerate scaling down capacity during those times. The goal is to minimize costs by paying only for what is used, without upfront commitments.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The SAA-C03 exam frequently reuses these exact scenarios with slightly different constraints.
✓Purchase a Compute Savings Plan for the expected steady hourly usage in that Region.Correct answer▾
Why this is correct
Compute Savings Plans offer lower hourly rates in exchange for a 1- or 3-year commitment, but the discount applies to any EC2 instance family/type/size in the chosen Region (even Fargate/Lambda). Because the recommendation engine runs 24/7, committing to the expected steady hourly usage captures the discount while preserving the ability to change instance families or sizes as needs evolve. Unlike Standard RIs, you're not locked into a specific instance type, so you get both cost savings and operational flexibility.
✗Switch the instances to Spot Instances and use interruption handling because it is the largest discount.Wrong answer — click to see why▾
Why this is wrong here
The workload is interruption-intolerant, so Spot Instances are unsuitable because they can be terminated with little notice, risking service disruption.
★ When this WOULD be the correct answer
A question where the workload is fault-tolerant, can handle interruptions (e.g., batch processing, data analysis), and cost reduction is the top priority, with no requirement for steady, uninterruptible compute.
Why candidates choose this
Candidates see 'largest discount' and assume Spot is always best for cost savings, overlooking the critical requirement of interruption intolerance.
✗Purchase a Standard Reserved Instance tied to a single specific instance type for the next 3 years.Wrong answer — click to see why▾
Why this is wrong here
A Standard Reserved Instance locks to a specific instance type, which conflicts with the requirement to change instance families and sizes during planned optimizations.
★ When this WOULD be the correct answer
A company has a predictable, steady-state workload that uses a specific instance type for 1-3 years, with no plans to change instance families or sizes, and seeks the maximum discount over On-Demand.
Why candidates choose this
Candidates may assume Reserved Instances always offer the best savings without considering the flexibility constraint, or they overlook the requirement to change instance types.
✗Keep On-Demand and rely on Auto Scaling to reduce capacity when utilization is low.Wrong answer — click to see why▾
Why this is wrong here
The workload is steady and interruption-intolerant, so Auto Scaling to reduce capacity when utilization is low would not provide the lowest cost for the steady baseline usage, and On-Demand pricing is more expensive than a Compute Savings Plan for predictable workloads.
★ When this WOULD be the correct answer
A company has a variable workload that experiences predictable low-usage periods (e.g., nightly or seasonal drops) and can tolerate scaling down capacity during those times. The goal is to minimize costs by paying only for what is used, without upfront commitments.
Why candidates choose this
Candidates may think Auto Scaling always reduces costs by matching capacity to demand, but they overlook that On-Demand pricing is still higher than savings plans for steady usage, and the question explicitly seeks the lowest cost.
Analysis generated from the official SAA-C03blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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