A is correct. On demand mode is for unknown load pattern, auto scaling is for know burst pattern

A on-demand prices can be 7 times higher, given the options it is better to have reserved WCU and RCU and auto scale in the given schedule

A is correct. The focus is minimizing the cost of tables.

Considering the application's need to handle a peak load that is double the average and the fact that the workload is write-heavy, option B (Configure on-demand capacity mode for the table) is the most suitable solution. It directly addresses the variability in workload without requiring upfront capacity planning or additional management overhead, thus likely providing the best cost optimization for this scenario. On-demand capacity mode eliminates the need to scale resources manually or through Auto Scaling and ensures that you only pay for the write and read throughput you consume.

A is badly worded however, because it says "application" autoscaling. We are not talking about that here. Either it should be reworded as "DynamoDB autoscaling" for the answer to be correct. On-demand capacity mode is for unknown read/write patterns. Since the load change patterns are known, anything that involves on-demand capacity modes can be eliminated (hence not B). DAX is a caching service deployed in front of DynamoDB. It is geared towards "performance at scale". Problem in the use case, is to optimize table costs. Using DAX will incur additional costs. Hence anything that involves DAX (C and D) can also be eliminated.

https://aws.amazon.com/blogs/database/amazon-dynamodb-auto-scaling-performance-and-cost-optimization-at-any-scale/#:~:text=You%20can%20approximate%20a%20blend,save%20money%20as%20reserved%20capacity

Option B is the most cost-effective solution for workloads with significant fluctuations and unpredictable access patterns. The on-demand capacity mode automatically adjusts the table’s throughput capacity as needed in response to actual traffic, eliminating the need to manually configure or manage capacity. This mode is ideal for applications with irregular traffic patterns, such as a significant peak once a week, because you only pay for the read and write requests your application performs, without having to provision throughput in advance. Option B directly addresses the requirement to minimize costs associated with fluctuating loads, especially when the load significantly exceeds the average only during a brief period, by leveraging DynamoDB’s on-demand capacity mode to automatically scale and pay only for what is used.

I think there is mistake in answer A, and it should be DynamoDb auto scaling instead of application autos calling. Or application and dynamoDB auto scaling.

I choose option D, because DAX is not only an accelerator for the Reads, it also cache releasing a lot of load from the DB.

A -> You can scale DynamoDB tables and global secondary indexes using target tracking scaling policies and scheduled scaling. In this I would go for scheduled scaling. https://docs.aws.amazon.com/autoscaling/application/userguide/services-that-can-integrate-dynamodb.html B -> on-demand capacity mode is for unknown workload, this is not the case C -> DAX come with costs and it helps with reads, while here we have a more write-bound workload D -> See B and C comments

we use scheduled scaling here

https://aws.amazon.com/blogs/database/amazon-dynamodb-auto-scaling-performance-and-cost-optimization-at-any-scale/#:~:text=You%20can%20approximate%20a%20blend,save%20money%20as%20reserved%20capacity.

Reserved capacity is available for single-Region, provisioned read and write capacity units (RCU and WCU) on DynamoDB tables including global and local secondary indexes. You cannot purchase reserved capacity for replicated WCUs (rWCUs).

Correct Answer: A Application auto scaling can be used for scheduled scaling for DynamoDB tables and GSIs https://docs.aws.amazon.com/autoscaling/application/userguide/what-is-application-auto-scaling.html

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Refer https://aws.amazon.com/dynamodb/reserved-capacity/ Reserved capacity is a great option to reduce DynamoDB costs for workloads with steady usage and predictable growth over time Reserved capacity mode might be best if you: Have predictable application traffic. Run applications whose traffic is consistent or ramps gradually. Can forecast capacity requirements to control costs.

A. This approach takes into account peak and average loads, but it might lead to unnecessary costs since you have to pay for reserved RCUs and WCUs, even during off-peak times. B. The on-demand capacity mode can adjust dynamically based on actual demand, making it a suitable option, especially considering the peak lasts only for 4 hours. C. DAX is designed to accelerate read operations, but the problem description indicates the access pattern is primarily write-focused. Therefore, this option might not be the best choice. D. This option combines DAX with the on-demand capacity mode, but as mentioned, DAX might not be necessary. Conclusion: Option B (configuring the table for on-demand capacity mode) seems to be the most appropriate choice, as it allows for dynamic capacity scaling during peaks and only pays for the required capacity costs during off-peak times.