Auto-scaling configuration in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding DynamoDB Auto-scaling Targets

Which of the following best describes the purpose of setting a target utilization percentage in DynamoDB auto-scaling?

A It defines the maximum number of read/write capacity units the table can have.

B It specifies the desired average utilization of provisioned capacity to maintain performance and cost balance.

C It sets the minimum capacity units the table must always have regardless of traffic.

D It determines the exact number of capacity units to allocate at all times.

💡 Hint

Think about how auto-scaling tries to balance cost and performance by adjusting capacity based on usage.

The target utilization percentage tells DynamoDB what average usage level to maintain. This helps auto-scaling increase or decrease capacity to keep performance steady without overspending.

❓ query_result

intermediate

Result of Auto-scaling Policy Update

Given a DynamoDB table with auto-scaling enabled and a target utilization of 70%, what happens if the actual consumed read capacity suddenly spikes to 90% for a sustained period?

A Auto-scaling gradually increases provisioned capacity to bring utilization closer to the 70% target.

B Auto-scaling disables itself to prevent over-provisioning.

C Auto-scaling immediately doubles the provisioned capacity to match the spike.

D Auto-scaling decreases provisioned capacity because the target utilization is exceeded.

💡 Hint

Consider how auto-scaling reacts to sustained changes rather than instant spikes.

Auto-scaling adjusts capacity gradually to avoid rapid fluctuations, increasing capacity to reduce utilization toward the target.

📝 Syntax

advanced

Valid JSON for Auto-scaling Configuration

Which JSON snippet correctly configures DynamoDB auto-scaling for read capacity with a target utilization of 75% and minimum capacity of 5 units?

A { "ScalableDimension": "dynamodb:table:ReadCapacityUnits", "MinCapacity": 5, "TargetTrackingScalingPolicyConfiguration": { "TargetValue": 75 } }

B { "ScalableDimension": "dynamodb:table:ReadCapacityUnits", "MinCapacity": "5", "TargetTrackingScalingPolicyConfiguration": { "TargetValue": 75 } }

C { "ScalableDimension": "dynamodb:table:ReadCapacityUnits", "MinCapacity": 5, "TargetTrackingScalingPolicyConfiguration": { "TargetValue": 0.75 } }

D { "ScalableDimension": "dynamodb:table:ReadCapacityUnits", "MinCapacity": 5, "TargetTrackingScalingPolicyConfiguration": { "TargetValue": "75" } }

💡 Hint

TargetValue expects a percentage value (e.g., 75) between 10 and 90 as a double. MinCapacity must be a number, not a string.

The TargetValue for DynamoDB auto-scaling is a percentage (e.g., 75 for 75%). MinCapacity must be a number, not a string.

❓ optimization

advanced

Optimizing Auto-scaling for Cost Efficiency

You notice your DynamoDB table's auto-scaling frequently scales up and down causing cost spikes. Which adjustment can reduce this oscillation?

A Set the minimum capacity to the highest observed usage.

B Lower the target utilization percentage to 30%.

C Increase the cooldown period between scaling actions.

D Disable auto-scaling and set a fixed high capacity.

💡 Hint

Think about how timing between scaling actions affects stability.

Increasing cooldown periods gives the system time to stabilize before another scaling action, reducing rapid up/down changes.

🔧 Debug

expert

Diagnosing Auto-scaling Failure

A DynamoDB table's write capacity is not scaling up despite high traffic. The auto-scaling policy is set with a target utilization of 70%, min capacity 5, max capacity 100. What is the most likely cause?

A The target utilization is set too low to trigger scaling.

B The table is in on-demand mode, so auto-scaling is ignored.

C The max capacity is set too high, preventing scaling.

D The IAM role used by auto-scaling lacks permission to update capacity.

💡 Hint

Check permissions when auto-scaling does not respond to load.

If the auto-scaling service cannot update capacity due to missing permissions, scaling will not occur despite high usage.