AWS Certified Solutions Architect - Associate
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A company performs tests on an application that uses an Amazon DynamoDB table. The tests run for 4 hours once a week. The company knows how many read and write operations the application performs to the table each second during the tests. The company does not currently use DynamoDB for any other use case. A solutions architect needs to optimize the costs for the table.
Which solution will meet these requirements?
Other
Community
UAnonymous
A
Choose on-demand mode. Update the read and write capacity units appropriately.
B
Choose provisioned mode. Update the read and write capacity units appropriately.
C
Purchase DynamoDB reserved capacity for a 1-year term.
D
Purchase DynamoDB reserved capacity for a 3-year term.
Explanation:
Explanation
Correct Answer: B - Choose provisioned mode. Update the read and write capacity units appropriately.
Why this is correct:
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Usage Pattern Analysis: The application runs tests for only 4 hours once a week. This is a highly predictable, intermittent workload with long periods of inactivity.
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Provisioned Mode Benefits:
- Cost Optimization: With provisioned mode, you pay for the capacity you provision regardless of usage. Since the company knows exactly how many read/write operations are needed during the 4-hour test window, they can provision exactly that capacity.
- No Unused Capacity Costs: During the remaining 164 hours of the week when no tests are running, the provisioned capacity costs are minimal compared to on-demand pricing.
- Predictable Billing: The company can accurately forecast costs based on their known test requirements.
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On-Demand Mode Drawbacks:
- On-demand mode charges per request, which would be more expensive for predictable, high-throughput workloads.
- Since the company knows their exact throughput requirements, they don't need the flexibility of on-demand scaling.
-
Reserved Capacity Drawbacks:
- Reserved capacity requires a commitment (1 or 3 years) and upfront payment.
- This is not cost-effective for a workload that only runs 4 hours per week.
- The company doesn't have other DynamoDB use cases, so the reserved capacity would be wasted most of the time.
Key Considerations:
- The company can use Auto Scaling with provisioned mode to automatically adjust capacity during the test window if needed.
- They can schedule capacity changes using AWS Lambda or CloudWatch Events to increase capacity just before tests and decrease it afterward.
- Since they know the exact throughput requirements, they can provision the minimum necessary capacity.
Cost Comparison:
- Provisioned Mode: Pay for 4 hours of provisioned capacity per week
- On-Demand Mode: Pay for actual requests during 4 hours, which would be higher for predictable high-throughput workloads
- Reserved Capacity: Pay upfront for capacity that would be unused 97% of the time
This solution provides the best cost optimization for this specific, predictable, intermittent workload pattern.
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