The answer is to use a Compute Savings Plan to cover the steady 24/7 baseline and run the nightly batch on Spot Instances. This is correct because a Compute Savings Plan applies a discounted rate to any EC2 instance family, region, or even container usage, providing the flexibility to change instance families during the year without losing the discount, while Spot Instances offer up to 90% savings for fault-tolerant, interruptible workloads like the checkpoint-resumable batch job. On the SAA-C03 exam, this scenario tests your ability to distinguish between Savings Plan types—Compute versus EC2 Instance—and to recognize that Spot Instances are ideal for stateless, resumable tasks, not for steady-state workloads. A common trap is choosing an EC2 Instance Savings Plan, which locks you to a specific family and would break the flexibility requirement. Memory tip: Compute Savings Plan covers the “core” steady load, while Spot handles the “spike” that can be stopped and started.
SAA-C03 Design Cost-Optimized Architectures Practice Question
This SAA-C03 practice question tests your understanding of design cost-optimized architectures. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
AWS Cost Explorer summary:
Baseline web tier: 8 instances running 24/7, average utilization 35%-45%
Nightly batch tier: 4 instances from 22:00-04:00 UTC
Batch logs:
22:14 UTC: Spot interruption notice received
22:14 UTC: checkpoint saved to S3
22:17 UTC: job resumed on new instance
Architecture notes:
Batch jobs are restartable and tolerate interruption
Operations wants freedom to switch instance families if needed
Based on the exhibit, the team wants to minimize compute cost for a workload with a steady 24/7 baseline and a separate nightly batch job that can be interrupted and resumed from checkpoints. They also expect to change EC2 instance families during the year as performance needs evolve. Which approach is the best fit?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
AWS Cost Explorer summary:
Baseline web tier: 8 instances running 24/7, average utilization 35%-45%
Nightly batch tier: 4 instances from 22:00-04:00 UTC
Batch logs:
22:14 UTC: Spot interruption notice received
22:14 UTC: checkpoint saved to S3
22:17 UTC: job resumed on new instance
Architecture notes:
Batch jobs are restartable and tolerate interruption
Operations wants freedom to switch instance families if needed
A
Buy EC2 Instance Savings Plans for the baseline and run the nightly batch on On-Demand instances.
Why wrong: Instance Savings Plans are flexible, but On-Demand batch instances waste money when the jobs explicitly tolerate interruption. This option does not fully exploit the restartable nature of the batch workload.
B
Use a Compute Savings Plan to cover the steady baseline and run the nightly batch on Spot Instances.
A Compute Savings Plan provides discount coverage while preserving flexibility across EC2 families and even other compute services. That makes it ideal for the steady baseline when future family changes are expected. Spot Instances are the lowest-cost choice for the restartable batch tier because interruptions are acceptable and checkpointing is already in place.
C
Purchase Standard Reserved Instances for all 12 instances and keep the current families fixed.
Why wrong: Reserved Instances can reduce cost, but they lock you into more specific EC2 characteristics. They are less flexible than a Compute Savings Plan and do not take advantage of Spot savings for interruption-tolerant batch work.
D
Run both tiers entirely on Spot Instances and rely on automatic restarts for the baseline web tier.
Why wrong: Spot can be cost-effective for interruptible batch jobs, but it is a poor choice for the 24/7 baseline web tier because capacity interruptions would affect availability and user experience. The baseline needs stable capacity.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a Compute Savings Plan to cover the steady baseline and run the nightly batch on Spot Instances.
Option B is correct because a Compute Savings Plan covers any EC2 instance family (or even container/Fargate usage) at a discounted rate, making it ideal for the steady 24/7 baseline. The nightly batch job can be interrupted and resumed from checkpoints, which is a perfect use case for Spot Instances, offering up to 90% cost savings. This combination minimizes compute cost while maintaining flexibility to change instance families during the year.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Buy EC2 Instance Savings Plans for the baseline and run the nightly batch on On-Demand instances.
Why it's wrong here
Instance Savings Plans are flexible, but On-Demand batch instances waste money when the jobs explicitly tolerate interruption. This option does not fully exploit the restartable nature of the batch workload.
✓
Use a Compute Savings Plan to cover the steady baseline and run the nightly batch on Spot Instances.
Why this is correct
A Compute Savings Plan provides discount coverage while preserving flexibility across EC2 families and even other compute services. That makes it ideal for the steady baseline when future family changes are expected. Spot Instances are the lowest-cost choice for the restartable batch tier because interruptions are acceptable and checkpointing is already in place.
Clue confirmation
The clue words "best", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Purchase Standard Reserved Instances for all 12 instances and keep the current families fixed.
Why it's wrong here
Reserved Instances can reduce cost, but they lock you into more specific EC2 characteristics. They are less flexible than a Compute Savings Plan and do not take advantage of Spot savings for interruption-tolerant batch work.
✗
Run both tiers entirely on Spot Instances and rely on automatic restarts for the baseline web tier.
Why it's wrong here
Spot can be cost-effective for interruptible batch jobs, but it is a poor choice for the 24/7 baseline web tier because capacity interruptions would affect availability and user experience. The baseline needs stable capacity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume Reserved Instances or Instance Savings Plans are always cheaper, but they fail to recognize that the requirement to change instance families during the year makes Compute Savings Plans the only flexible discount option, and they overlook that Spot Instances are ideal for interruptible batch jobs.
Detailed technical explanation
How to think about this question
Compute Savings Plans apply to any EC2 instance, regardless of family, size, region (within the same AWS account), or even AWS Fargate and Lambda usage, providing up to 66% discount compared to On-Demand. Spot Instances use spare EC2 capacity and can be interrupted with a 2-minute notification, but the batch job's checkpointing capability allows it to resume seamlessly, making it cost-effective. A common real-world scenario is a data processing pipeline that uses Spot Instances for transient workloads while a web server fleet runs under a Compute Savings Plan to absorb pricing fluctuations.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Design Cost-Optimized Architectures — This question tests Design Cost-Optimized Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a Compute Savings Plan to cover the steady baseline and run the nightly batch on Spot Instances. — Option B is correct because a Compute Savings Plan covers any EC2 instance family (or even container/Fargate usage) at a discounted rate, making it ideal for the steady 24/7 baseline. The nightly batch job can be interrupted and resumed from checkpoints, which is a perfect use case for Spot Instances, offering up to 90% cost savings. This combination minimizes compute cost while maintaining flexibility to change instance families during the year.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best", "minimum / minimize". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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