A startup's DynamoDB table serves a workload with highly unpredictable traffic spikes tied to viral social media mentions, and the team does not want to forecast capacity or manage scaling policies. Which DynamoDB capacity mode best fits this workload?
- Provisioned capacity with no auto scaling configured
- On-demand capacity mode, which bills per request and adapts instantly to traffic changes
- Provisioned capacity fixed at the account's maximum throughput
- Reserved capacity purchased for a one-year term
Why B? And why not the others?
Correct answer: B. On-demand capacity mode, which bills per request and adapts instantly to traffic changes
On-demand capacity mode charges per read and write request rather than for pre-allocated throughput, and DynamoDB automatically accommodates traffic increases without the customer setting or adjusting any read or write capacity units, making it well suited to workloads with sudden, hard-to-predict spikes like a viral event. The option describing provisioned capacity with no auto scaling is wrong because a fixed provisioned throughput number would throttle requests the moment traffic exceeds it, which is exactly the risk with unpredictable spikes. The option describing provisioned capacity fixed at the account maximum is wrong because permanently reserving the account's maximum throughput would be extremely wasteful and costly during normal, low-traffic periods, and DynamoDB capacity is not something reserved at the account level this way. The option describing a one-year reserved capacity purchase is wrong because reserved capacity commitments are a cost-optimization tool for steady, predictable baseline usage, which is the opposite of the described spiky, unpredictable workload.
Source: AWS DynamoDB documentation: read/write capacity modes