Quick Answer
The answer is On-Demand Instances. This is the correct EC2 purchasing option for variable traffic workloads because it provides full flexibility with no upfront commitment or long-term contract, allowing you to scale capacity up and down instantly as demand fluctuates without incurring penalties or overpaying for idle resources. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your ability to match purchasing models to workload patterns—specifically, that variable traffic requires pay-as-you-go pricing to optimize costs without sacrificing performance. A common trap is choosing Savings Plans or Reserved Instances, which offer lower per-hour rates but lock you into a 1- or 3-year commitment, making them unsuitable for unpredictable usage. Spot Instances are also a distractor, but they can be interrupted, which breaks the consistent availability required for a web application behind an ALB. Memory tip: think “On-Demand for on-and-off demand”—if your traffic is unpredictable, pay only for what you use, no strings attached.
This SOA-C02 practice question tests your understanding of cost and performance optimization. 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.
A company is running a web application on EC2 instances behind an Application Load Balancer. The application experiences variable traffic patterns. The SysOps team wants to optimize costs without impacting performance. Which EC2 purchasing option should the team use for the instances?
Savings Plans
Why wrong: Cost savings require commitment; traffic variability may still need flexibility.
Spot Instances
Why wrong: Prone to interruption; not suitable for a web application requiring high availability.
On-Demand Instances
No upfront commitment, fits variable traffic patterns perfectly.
Reserved Instances
Why wrong: Requires 1- or 3-year commitment, not ideal for variable traffic.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
On-Demand Instances
Option C is correct because On-Demand instances provide flexibility and no upfront commitment, suitable for variable traffic. Savings Plans offer lower prices but require a 1- or 3-year commitment, which may not align with variable patterns. Reserved Instances also require commitment. Spot Instances are not suitable for a web application that needs consistent availability.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Savings Plans
Why it's wrong here
Cost savings require commitment; traffic variability may still need flexibility.
Spot Instances
Why it's wrong here
Prone to interruption; not suitable for a web application requiring high availability.
On-Demand Instances
Why this is correct
No upfront commitment, fits variable traffic patterns perfectly.
Related concept
Static NAT maps one inside address to one outside address.
Reserved Instances
Why it's wrong here
Requires 1- or 3-year commitment, not ideal for variable traffic.
Common exam traps
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
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
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SOA-C02 NAT questions on configuration and troubleshooting.
Cost and Performance Optimization — study guide chapter
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FAQ
Cost and Performance Optimization — This question tests Cost and Performance Optimization — Static NAT maps one inside address to one outside address..
The correct answer is: On-Demand Instances — Option C is correct because On-Demand instances provide flexibility and no upfront commitment, suitable for variable traffic. Savings Plans offer lower prices but require a 1- or 3-year commitment, which may not align with variable patterns. Reserved Instances also require commitment. Spot Instances are not suitable for a web application that needs consistent availability.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SOA-C02 NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 20, 2026
This SOA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SOA-C02 exam.
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