SAP-C02 Practice Question 28: Commitment Discounts Changing Fleet
AWS Certified Solutions Architect – Professional (SAP-C02) · Test 3 · question 8 of 10
A company's monthly compute bill is roughly 60 percent Amazon EC2 On-Demand across eight instance families in three Regions, 25 percent AWS Fargate, and 15 percent AWS Lambda. Cost Explorer shows a steady floor of EC2 usage that never drops below about 70 percent of the monthly average, plus a nightly batch job (fault tolerant, restartable, and free to run on any instance type) that accounts for most of the variability.
Over the next 12 months, three teams will containerize their EC2 workloads and move them to Fargate, and the platform team expects to change instance families as newer generations appear. Finance wants the largest discount it can get, but the CFO has explicitly refused any commitment that could end up unused if the migration to Fargate runs ahead of schedule, and refuses to commit to specific instance families.
Which purchasing strategy should the architect recommend?
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Answer:
A Compute Savings Plan is the only commitment in the list whose discount follows the workload wherever it goes: it applies to EC2 usage regardless of instance family, size, operating system, tenancy, or Region, and it also applies to Fargate and Lambda usage. That means the dollars committed keep earning the discount as teams containerize onto Fargate and as the platform team rolls to newer instance generations, which is what removes the CFO's stranded-commitment risk. Sizing the commitment to the usage floor rather than to peak is the other half of that protection: nothing above the floor is committed, so nothing can go unused. The variable portion is then handled where the workload allows it; a fault-tolerant, restartable, instance-agnostic batch job is the textbook Spot candidate, and a mixed-instances Auto Scaling group spreads it across many instance types so a single capacity reclamation does not stall the run.
Option A is the most locked-in choice available: Standard Reserved Instances cannot be exchanged for a different family, three years is well past the migration horizon, and none of that commitment covers Fargate or Lambda. Every workload that moves to a container strands its RI.
Option B has the same family lock-in, just in Savings Plan form. EC2 Instance Savings Plans commit to an instance family in a single Region and, unlike Compute Savings Plans, do not apply to Fargate or Lambda at all.
Option C is closer, Convertible RIs can be exchanged, but exchanges are a manual, ongoing chore, they still cover only EC2, and sizing the commitment to *peak* rather than to the floor guarantees unused commitment on quiet days, which is what the CFO refused.
Reference: What are Savings Plans?