A web service runs continuously on AWS 24/7. The team expects steady compute usage for the next 12–24 months, but may change instance families/sizes as performance tuning continues. Which purchase option best reduces cost while keeping flexibility to change instance types?

Buy EC2 On-Demand instances and rely on future Spot capacity for discounts

On-Demand pricing has no commitment-based discount, so a steady 24/7 workload generally remains costly. Relying on future Spot capacity does not match the predictable continuous demand and may also introduce interruptions unless the architecture is designed for them.

Buy Reserved Instances with a fixed instance type and region

Instance-specific Reserved Instances discount On-Demand but require matching the specified instance family/size and scope constraints. Frequent changes to instance families/sizes can reduce or prevent using the committed discount effectively.

Buy Spot Instances and stop scaling to avoid interruption risk

Spot provides lower pricing but can be interrupted when capacity is reclaimed. Stopping scaling does not remove interruption risk; it only changes how capacity is adjusted. For a 24/7 service, this can still cause outages unless substantial fault-tolerance is built.

What does this SAA-C03 question test?

Read the scenario before looking for a memorised answer.

What is the correct answer to this question?

The correct answer is: Use Compute Savings Plans for the expected steady usage — Compute Savings Plans are the best fit for a workload with steady compute usage over a 12–24 month term where the team wants to change instance families/sizes during optimization. Savings Plans lower costs with a usage commitment, and Compute Savings Plans are the most flexible type because the discounted usage can apply across EC2 instance families and sizes rather than being tied to one specific configuration. The other choices either do not provide a commitment discount for predictable steady usage (On-Demand), are too restrictive for frequent instance changes (instance-specific Reserved Instances), or introduce interruption risk inappropriate for an always-on service without additional design work (Spot). Why others are wrong: On-Demand provides no commitment-based discount, so it does not address the cost goal for predictable 24/7 usage. Instance-specific Reserved Instances can become misaligned when instance families/sizes change during tuning, reducing effective coverage. Spot offers discounts but can be interrupted regardless of scaling behavior; a 24/7 service would still need interruption tolerance that isn’t stated in the scenario.

What should I do if I get this SAA-C03 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.