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.

Practice

1. What is the main purpose of auto-scaling in DynamoDB?

easy

A. To encrypt data stored in the table

B. To manually set fixed capacity limits

C. To backup data at regular intervals

D. To automatically adjust read and write capacity based on traffic

Solution

1. Step 1: Understand auto-scaling function

   Auto-scaling automatically changes capacity to match traffic demands.

2. Step 2: Compare options

   Only To automatically adjust read and write capacity based on traffic describes automatic adjustment of capacity based on traffic.

3. Final Answer:

   To automatically adjust read and write capacity based on traffic -> Option D

4. Quick Check:

   Auto-scaling adjusts capacity automatically = A [OK]

Hint: Auto-scaling means automatic capacity adjustment [OK]

Common Mistakes:

• Confusing auto-scaling with manual capacity setting
• Thinking auto-scaling handles backups
• Mixing encryption with scaling

2. Which of the following is the correct way to specify the minimum capacity units in a DynamoDB auto-scaling policy JSON snippet?

easy

A. "MinCapacity": 5

B. "MinimumCapacityUnits": 5

C. "min_capacity": 5

D. "Min_Capacity": 5

Solution

1. Step 1: Recall DynamoDB auto-scaling JSON keys

   The correct key for minimum capacity is "MinCapacity" with camel case and no underscores.

2. Step 2: Check options

   Only "MinCapacity": 5 matches the exact key syntax "MinCapacity".

3. Final Answer:

   "MinCapacity": 5 -> Option A

4. Quick Check:

   Correct JSON key for minimum capacity = B [OK]

Hint: Use exact key names with correct casing in JSON [OK]

Common Mistakes:

• Using underscores instead of camel case
• Adding extra words like 'Units'
• Incorrect capitalization

3. Given this auto-scaling target tracking policy snippet:

{
  "TargetValue": 70.0,
  "ScaleInCooldown": 60,
  "ScaleOutCooldown": 60
}

What does the TargetValue represent?

medium

A. The maximum capacity units allowed

B. The cooldown time in seconds

C. The desired utilization percentage of capacity

D. The minimum capacity units allowed

Solution

1. Step 1: Understand TargetValue meaning

   TargetValue sets the target utilization percentage for capacity usage.

2. Step 2: Analyze options

   The desired utilization percentage of capacity correctly describes TargetValue as desired utilization percent (70%).

3. Final Answer:

   The desired utilization percentage of capacity -> Option C

4. Quick Check:

   TargetValue = utilization percent = C [OK]

Hint: TargetValue sets target usage percent, not capacity units [OK]

Common Mistakes:

• Confusing TargetValue with capacity limits
• Mixing cooldown times with TargetValue
• Thinking TargetValue is a fixed capacity number

4. You have this auto-scaling policy JSON snippet:

{
  "MinCapacity": 5,
  "MaxCapacity": 100,
  "TargetValue": 80.0,
  "ScaleInCooldown": 30,
  "ScaleOutCooldown": 30
}

But the policy is not working as expected. What is the likely error?

medium

A. MinCapacity is greater than MaxCapacity

B. Missing required field for resource ID

C. TargetValue should be between 0 and 1, not 80.0

D. Cooldown times are too short and cause rapid scaling

Solution

1. Step 1: Check capacity and cooldown values

   MinCapacity (5) is less than MaxCapacity (100), cooldowns are valid numbers.

2. Step 2: Identify missing required fields

   Auto-scaling policies require resource identifiers (like ResourceId) to apply the policy.

3. Step 3: Confirm TargetValue range

   TargetValue is a percentage and 80.0 is valid.

4. Final Answer:

   Missing required field for resource ID -> Option B

5. Quick Check:

   Missing resource ID causes policy failure = A [OK]

Hint: Check for all required fields, not just values [OK]

Common Mistakes:

• Assuming cooldown times cause failure
• Misreading TargetValue scale
• Ignoring missing resource identifiers

5. You want to configure auto-scaling for a DynamoDB table with unpredictable traffic spikes. Which combination of settings will best ensure smooth scaling without throttling or overspending?

{
  "MinCapacity": 10,
  "MaxCapacity": 200,
  "TargetValue": 70.0,
  "ScaleInCooldown": 120,
  "ScaleOutCooldown": 30
}

hard

A. Set a low MinCapacity, high MaxCapacity, fast ScaleOutCooldown, slow ScaleInCooldown

B. Set MinCapacity equal to MaxCapacity for fixed capacity

C. Set very fast ScaleInCooldown and ScaleOutCooldown both to 10 seconds

D. Set TargetValue to 100 to maximize usage

Solution

1. Step 1: Understand traffic spikes impact

   Unpredictable spikes need quick scaling out to avoid throttling and slower scaling in to avoid rapid capacity drops.

2. Step 2: Analyze given settings

   Low MinCapacity saves cost, high MaxCapacity allows growth, fast ScaleOutCooldown (30s) reacts quickly, slow ScaleInCooldown (120s) prevents rapid scale down.

3. Step 3: Evaluate other options

   Fixed capacity ignores spikes, very fast cooldowns cause thrashing, setting TargetValue to 100 risks overprovisioning.

4. Final Answer:

   Set a low MinCapacity, high MaxCapacity, fast ScaleOutCooldown, slow ScaleInCooldown -> Option A

5. Quick Check:

   Fast scale out + slow scale in = smooth scaling = D [OK]

Hint: Fast scale out, slow scale in for spike handling [OK]

Common Mistakes:

• Setting fixed capacity ignoring spikes
• Using equal cooldowns causing rapid scaling
• Setting TargetValue too high causing overspending