SOA-C02 Cost and Performance Optimization Practice Question
A company uses an Amazon DynamoDB table with on-demand capacity mode for a variable workload. The SysOps administrator notices high costs and wants to reduce them without affecting application performance. Which action should the administrator take?
⚠ Common exam trap
Watch out — candidates often assume on-demand mode is always the most cost-effective for variable workloads, but the exam tests that provisioned capacity with auto scaling can be cheaper for predictable variability, and that options like DAX or TTL address different cost components (latency or storage) rather than the per-request compute cost.
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
✓
Switch the table to provisioned capacity mode with auto scaling.
Switching from on-demand to provisioned capacity with auto scaling reduces costs for variable workloads by allowing you to set a lower base capacity and scale only when needed, avoiding the premium per-request pricing of on-demand mode. Auto scaling adjusts read/write capacity based on actual utilization, ensuring application performance is maintained while eliminating the cost overhead of paying for every request at on-demand rates.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Switch the table to provisioned capacity mode with auto scaling.
Why this is correct
On-demand capacity mode charges per request and is ideal for unpredictable traffic, but for workloads with steady or moderately variable usage, provisioned capacity with auto scaling is significantly cheaper because you commit to a baseline of capacity units and pay only for what you provision, while auto scaling adjusts the provisioned throughput based on real-time utilization via CloudWatch alarms, preventing over-provisioning and reducing cost without manual intervention.
- ✗
Enable DynamoDB Accelerator (DAX) for caching.
Why it's wrong here
DAX is an in-memory cache that offloads reads from the DynamoDB table, reducing the number of read capacity units consumed; however, DAX itself incurs per-node hourly charges and is an additional service, so enabling it does not reduce the cost of the table's underlying capacity modes and, in fact, adds a new cost component without directly addressing the primary drivers of expense in on-demand mode, which are read and write request units.
- ✗
Implement DynamoDB Global Tables to distribute data across regions.
Why it's wrong here
Global Tables replicate data synchronously across multiple AWS Regions, and every write to any replica consumes write capacity units in each Region where the table is replicated, effectively multiplying write costs by the number of replicas; this also increases storage costs because each replica stores a full copy of the table, so implementing Global Tables is a disaster-recovery or low-latency feature that directly increases operational cost, not a cost optimization measure.
- ✗
Set a Time to Live (TTL) attribute to automatically expire old items.
Why it's wrong here
TTL automatically deletes expired items at no extra cost and helps reduce storage footprint, but in on-demand capacity mode, the dominant cost is read and write request units, not storage; because TTL deletions do not consume write capacity units and storage charges are typically a small fraction of total DynamoDB cost, setting TTL will have minimal impact on the table's overall expense compared to changing capacity modes or reducing unnecessary reads/writes.
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Same concept, more angles
2 more ways this is tested on SOA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses an Amazon DynamoDB table with on-demand capacity mode. The table handles a workload with a steady baseline of 500 writes per second but spikes to 2,000 writes per second for a few hours each day. The SysOps administrator wants to reduce costs without affecting application performance during spikes. Which action should the administrator take?
medium- ✓ A.Switch to provisioned capacity with auto scaling to handle the spikes.
- B.Enable DynamoDB Accelerator (DAX) to cache reads.
- C.Create a global table to distribute write traffic.
- D.Use Amazon ElastiCache to buffer write requests.
Why A: On-demand capacity mode is ideal for unpredictable workloads but costs more per write than provisioned capacity. Since this workload has a predictable baseline and spikes, switching to provisioned capacity with auto scaling allows you to pay a lower rate for the steady 500 writes per second while auto scaling automatically adds capacity to handle the 2,000 writes per second spikes, reducing overall cost without impacting performance.
Variation 2. 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?
medium- ✓ A.Enable DynamoDB auto scaling
- B.Switch to DynamoDB on-demand capacity mode
- C.Purchase reserved capacity for 2,000 WCU
- D.Use DynamoDB Time to Live (TTL) to delete old items
Why A: 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.
JA
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.