SOA-C02 Cost and Performance Optimization Practice Question
A company uses an Amazon DynamoDB table with provisioned capacity. The average write usage is 500 write capacity units (WCU) but regularly spikes to 2,000 WCU during business hours. The SysOps administrator wants to reduce costs without affecting performance during the spikes. Which solution should the administrator implement?
⚠ Common exam trap
Many exam-takers confuse on-demand mode as a cost-saving measure for spiky workloads, but in reality, on-demand is more expensive than provisioned capacity with auto scaling when there is a predictable baseline, and the question specifically asks to reduce costs without affecting performance.
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
✓
Enable DynamoDB auto scaling
DynamoDB auto scaling allows the table to automatically adjust its provisioned write capacity between a minimum and maximum range based on actual traffic. By setting the minimum WCU to cover the average usage (500) and the maximum to handle the spikes (2,000), the administrator pays only for the baseline capacity most of the time, while the service scales up during spikes without manual intervention or over-provisioning.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Enable DynamoDB auto scaling
Why this is correct
DynamoDB auto scaling uses CloudWatch metrics (ConsumedWriteCapacityUnits and ConsumedReadCapacityUnits) to automatically adjust provisioned capacity between configured minimum and maximum limits. This handles predictable spikes by scaling up in advance and reduces costs by scaling down during low usage, eliminating manual intervention. With a target utilization set (e.g., 70%), auto scaling maintains enough capacity to handle demand while avoiding overprovisioning.
- ✗
Switch to DynamoDB on-demand capacity mode
Why it's wrong here
On-demand capacity mode bills per read/write request with no upfront commitment and automatically accommodates any level of traffic. However, it is more expensive per request than provisioned capacity and is best suited for unpredictable workloads or new applications with unknown usage patterns. For a workload with predictable spikes and an otherwise steady baseline, auto scaling on provisioned capacity provides the required burst capability at a lower total cost.
- ✗
Purchase reserved capacity for 2,000 WCU
Why it's wrong here
Reserved capacity is a billing discount applied to provisioned throughput, requiring a 1- or 3-year commitment to a specific number of read and write capacity units. Purchasing reserved capacity for 2,000 WCU locks you into paying for that throughput even when the table's average usage is far lower, leading to wasted spend. It also does not automatically handle spikes beyond the reserved amount and does not replace the need for auto scaling to manage dynamic demand.
- ✗
Use DynamoDB Time to Live (TTL) to delete old items
Why it's wrong here
Time to Live (TTL) automatically deletes items after a specified timestamp, reducing storage costs and keeping the table from accumulating stale data. These deletions are processed asynchronously and consume write capacity units for each delete, but TTL has no effect on the table's throughput settings or the need to handle spikes in incoming write requests. It addresses data lifecycle management, not capacity planning or cost optimization for write traffic.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SOA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SOA-C02 exam.