SOA-C02 Cost and Performance Optimization Practice Question
A SysOps administrator manages a web application running on Amazon EC2 instances that run 24/7 for the next 12 months. The workload is steady and predictable. Which EC2 purchasing option provides the highest cost savings for this use case?
⚠ Common exam trap
Many candidates choose Savings Plans (Compute) because they offer flexibility across instance families, but for a predictable, steady-state workload with a fixed instance type, Standard Reserved Instances provide the highest discount and capacity guarantee, making them the optimal choice for cost savings.
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
✓
Standard Reserved Instances
Standard Reserved Instances provide the highest cost savings for a steady, predictable 24/7 workload over a 12-month period because they offer a significant discount (up to 72% compared to On-Demand) in exchange for a commitment to a specific instance family, region, and term length. Since the workload runs continuously without interruption, the upfront payment or partial upfront payment for a 1-year term maximizes savings without the risk of interruption or the need for flexibility.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Standard Reserved Instances
Why this is correct
Standard Reserved Instances are ideal for a steady, predictable 24/7 workload because they offer the deepest discount, up to 72% compared to On-Demand, when you commit to a 1-year or 3-year term. You can choose All Upfront, Partial Upfront, or No Upfront payment options, which further optimize cash flow while locking in the lowest hourly rate for a specific instance family and region. For a workload that runs continuously without interruption, this commitment maximizes cost savings while guaranteeing capacity, making it the most economical choice.
- ✗
Spot Instances
Why it's wrong here
Spot Instances provide spare Amazon EC2 compute capacity at discounts of up to 90% versus On-Demand, but AWS can reclaim that capacity with only a two-minute warning when it needs the resources back. This makes them unsuitable for a 24/7 web application that requires high availability and consistent response times, as any interruption would cause an immediate outage or force clients to retry. Spot Instances are designed for fault-tolerant, stateless workloads such as batch processing, CI/CD, or data analysis, not for always-on production services.
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On-Demand Instances
Why it's wrong here
On-Demand Instances let you pay per second with no upfront commitment or long-term contract, offering maximum flexibility but at the highest cost among all purchasing options. For a web application that runs 24/7, every hour accumulates at the full On-Demand rate, leading to unnecessarily high monthly bills when compared to Reserved Instances or Savings Plans. Since the workload is constant and predictable, paying the full price for every hour without any volume discount is financially inefficient, making On-Demand the least cost-optimized choice for this scenario.
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Savings Plans (Compute)
Why it's wrong here
Compute Savings Plans offer lower EC2 hourly rates in exchange for a 1-year or 3-year commitment, but they provide up to 66% savings compared to On-Demand, which is less than the up to 72% available with Standard Reserved Instances. Their flexibility lets you change instance family, size, region, OS, or even run Fargate, which is valuable for dynamic workloads but not needed for a fixed, steady-state web application. For a workload that never changes and runs continuously, the higher discount and lower absolute cost of Standard Reserved Instances make Compute Savings Plans a suboptimal, though still cost-saving, option.
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