SAA-C03 Design Cost-Optimized Architectures Practice Question
A media company runs a fleet of EC2 instances using Auto Scaling across multiple instance families (for example, m-series and c-series) in a single region. The business wants to commit to steady usage for one year to reduce cost, but the application team must retain flexibility to switch instance families and scale up/down as demand changes. They need the cost-reduction approach that best matches this flexibility. Which option is the best fit?
⚠ Common exam trap
Many exam-takers confuse Reserved Instances (which lock to a specific family) with Savings Plans (which offer family flexibility), leading them to choose Option A despite the requirement for instance family switching.
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 Compute Savings Plans so the commitment applies regardless of instance family changes within the selected scope.
Compute Savings Plans provide the most flexibility because they apply to any EC2 instance family (including m-series and c-series) within a region, automatically adjusting to instance family changes and scaling. This matches the requirement to commit to steady usage for one year while retaining the ability to switch families and scale up/down, offering up to 66% savings over On-Demand without locking the application to a specific instance type.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Purchase Standard Reserved Instances tied to a specific instance family and region, so the application can only run on the selected family.
Why it's wrong here
Standard Reserved Instances can be scoped to specific attributes (such as instance family/size depending on the RI type). This conflicts with the requirement to freely switch instance families because the discounted capacity primarily applies to the specific scope you purchase.
- ✓
Purchase Compute Savings Plans so the commitment applies regardless of instance family changes within the selected scope.
Why this is correct
Compute Savings Plans provide discounted pricing in exchange for a 1-year or 3-year commitment, while allowing flexibility across instance families/attributes within the scope (for example, region/account and covered usage). This aligns with Auto Scaling that may shift between instance families while maintaining steady overall compute usage.
- ✗
Purchase Spot Instances for all capacity and disable On-Demand fallback to guarantee the lowest cost.
Why it's wrong here
Spot is not a commitment-based pricing model and cannot guarantee capacity availability. Disabling On-Demand fallback increases the risk of failed capacity during Spot interruptions or capacity shortages, which does not match the goal of stable one-year cost reduction for steady usage.
- ✗
Rely only on On-Demand and reduce cost by using a CloudFront-only approach for all dynamic content.
Why it's wrong here
CloudFront can reduce delivery costs for cached content, but it does not replace or discount EC2 compute pricing for dynamic workloads in the general case. This option also does not satisfy the requirement to commit for one year to reduce EC2 cost through a pricing commitment instrument.
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