AWS Certified Solutions Architect Professional SAP-C02 Practice Question
A company runs a latency-sensitive analytics engine on ten r6g.xlarge Amazon EC2 instances in the us-east-1a Availability Zone. The workload is steady 24 hours a day and cannot tolerate capacity shortages or instance interruptions. Architects expect to migrate the engine to r7g instances within the next 12 months.
The company also:
hosts containerized microservices on AWS Fargate that average USD 300 per hour of compute usage, and
performs a nightly ETL job on c7g.4xlarge Spot Instances that can be interrupted.
Finance wants to minimize compute costs for the next 3 years while guaranteeing capacity for the analytics engine in us-east-1a and keeping future migrations flexible.
Which combination of AWS purchasing options meets these requirements?
Create an On-Demand Capacity Reservation for ten r6g.xlarge instances in us-east-1a and purchase a 3-year Compute Savings Plan sized for the combined analytics and Fargate baseline; continue running the ETL job on Spot Instances.
Purchase a 3-year Compute Savings Plan sized for the r6g fleet and the Fargate usage; continue running the ETL job on Spot Instances.
Purchase ten 3-year No-Upfront Convertible Reserved Instances scoped to us-east-1a for the r6g fleet; purchase a 3-year Compute Savings Plan sized only for the Fargate usage; continue running the ETL job on Spot Instances.
Purchase ten 3-year Standard Regional Reserved Instances for r6g.xlarge; pay On-Demand pricing for Fargate; continue running the ETL job on Spot Instances.
The correct approach is to reserve capacity for the critical r6g fleet and apply the largest available discount across all steady-state compute usage:
On-Demand Capacity Reservation (ODCR) in us-east-1a guarantees that ten r6g.xlarge instances are always available, satisfying the no-shortage requirement.
A 3-year Compute Savings Plan attaches its discount to the running instances inside the ODCR and simultaneously covers the Fargate workload. Compute Savings Plans provide up to a 66 % discount, apply automatically to any instance family (including r6g today and r7g after migration), and extend to Fargate usage-all without additional exchanges.
Spot Instances remain the most cost-effective choice for the interruptible ETL job.
Other options fall short:
A Compute Savings Plan alone offers no capacity reservation, so it cannot protect against shortages.
Zonal Convertible Reserved Instances do reserve capacity and allow family exchanges, but their maximum discount (≈ 54 %) is smaller than the combined ODCR + Compute SP approach, so they do not minimize cost.
Standard Regional Reserved Instances give a higher discount but provide no capacity reservation and cannot shift to r7g, risking shortages or migration penalties.
Therefore, combining an ODCR with a Compute Savings Plan and keeping the ETL workload on Spot Instances best satisfies cost, performance, and flexibility goals.
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