Exam AWS Certified Solutions Architect - Associate SAA-C03 topic 1 question 79 discussion

On-demand mode is a good option if any of the following are true: - You create new tables with unknown workloads. - You have unpredictable application traffic. - You prefer the ease of paying for only what you use.

**A** - On demand is the answer - https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.ReadWriteCapacityMode.html#HowItWorks.OnDemand B - not related with the unpredictable traffic C - provisioned capacity is recommended for known patterns. Not the case here. D - same as C

The correct answer is A, keyword "unpredictable workloads"

Unknown Load/traffic = On demand mode

On-demand mode of DynamoDB is the most suitable for unpredictable workloads.

after browsing through all the responses, I decided to vote for C for the following 2 reasons: - Unpredictable traffic: Since the evening traffic is often unpredictable with quick spikes, using provisioned capacity with auto scaling allows the table to automatically adjust to meet the fluctuating demand, preventing potential throttling issues during high traffic periods. - Cost optimization: By utilizing auto scaling, the company only pays for the capacity it actually uses, which is ideal for a scenario where the table experiences low usage during mornings and high, unpredictable usage in the evenings.

Ans A - handles unpredictable workloads/traffic; pay on demand C - provisioned capacity for known data I/O - not the case here

Unpredictable = On-demand

cost is concern so CD are not right as provisioning is costly B is irrelevant A on-demand is correct as it will scale according to the usage pattern which is from low to very abrupt high

Choosing the On-Demand Capacity model (Option A) may cause performance issues during peak periods because it relies on DynamoDB to automatically adjust throughput based on actual usage, which may not be able to cope with sudden traffic increases in time. Choosing a DynamoDB table with a global secondary index (option B) is independent of the capacity model and does not directly solve the problem of peak traffic. Choosing to build DynamoDB tables in provisioned capacity mode and configure them as global tables (option D) may increase costs in some cases without necessarily providing the flexibility to accommodate unpredictable peak traffic.

DynamoDB autoscaling takes 2 minutes to increase capacity. We need to handle it immediately. "Application Auto Scaling automatically scales the provisioned capacity only when the consumed capacity is higher than target utilization for two consecutive minutes". https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/TroubleshootingThrottling.html

The costly part of (C) is you need to pay for what you order not what you have used for (A) On-Demand: A reserved capacity purchase is an agreement to pay for a minimum amount of provisioned throughput capacity, for the duration of the term of the agreement, in exchange for discounted pricing. If you use less than your reserved capacity, you will still be charged each month for that minimum amount of provisioned throughput capacity.

https://docs.aws.amazon.com/wellarchitected/latest/serverless-applications-lens/capacity.html With on-demand capacity mode, DynamoDB charges you for the data reads and writes your application performs on your tables. You do not need to specify how much read and write throughput you expect your application to perform because DynamoDB instantly accommodates your workloads as they ramp up or down. With provisioned capacity mode, you specify the number of reads and writes per second that you expect your application to require, and you are billed based on that. Furthermore if you can forecast your capacity requirements you can also reserve a portion of DynamoDB provisioned capacity and optimize your costs even further.

With on-demand capacity mode, DynamoDB instantly accommodates your workloads as they ramp up or down.

on-demand capacity : unpredictable application traffic provisioned capacity : predictable application traffic, run applications whose traffic is consistent, and ramps up or down gradually. https://docs.aws.amazon.com/wellarchitected/latest/serverless-applications-lens/capacity.html

By choosing provisioned capacity, you can allocate a specific amount of read and write capacity units based on your expected usage during peak times. This helps in cost optimization as you only pay for the provisioned capacity, which can be adjusted according to your anticipated traffic. Enabling auto scaling allows DynamoDB to automatically adjust the provisioned capacity up or down based on the actual usage. This is beneficial in handling quick traffic spikes without manual intervention and ensuring that the required capacity is available to handle increased load efficiently. Auto scaling helps to optimize costs by dynamically adjusting the capacity to match the demand, avoiding overprovisioning during periods of low usage. A. Creating a DynamoDB table in on-demand capacity mode, may not be the most cost-effective solution in this scenario. On-demand capacity mode charges you based on the actual usage of read and write requests, which can be beneficial for sporadic or unpredictable workloads. However, it may not be the optimal choice if the table is not used on most mornings.

Correct answer is A - You create new tables with unknown workloads. - You have unpredictable application traffic. - You prefer the ease of paying for only what you use.