CloudWatch metrics for DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Read Capacity Units (RCUs) in DynamoDB CloudWatch Metrics

Which CloudWatch metric indicates the number of strongly consistent reads consumed per second by a DynamoDB table?

A ConsumedWriteCapacityUnits

B ConsumedReadCapacityUnits

C ReadThrottleEvents

D WriteThrottleEvents

💡 Hint

Think about the metric that tracks read operations usage.

The ConsumedReadCapacityUnits metric shows the number of read capacity units consumed per second, including strongly consistent reads.

❓ query_result

intermediate

Interpreting Throttling Events from CloudWatch Metrics

If a DynamoDB table's CloudWatch metric WriteThrottleEvents shows a value greater than zero, what does this indicate?

A The table is underutilized and has spare write capacity.

B The table has no write activity.

C The table is experiencing throttling on write requests due to exceeding provisioned capacity.

D The table's read requests are being throttled.

💡 Hint

Focus on what throttling means in DynamoDB context.

WriteThrottleEvents counts the number of write requests that were throttled because the table exceeded its provisioned write capacity.

📝 Syntax

advanced

Correct CloudWatch Metric Name for DynamoDB Table Size

Which of the following is the correct CloudWatch metric name to monitor the total size of a DynamoDB table in bytes?

A TableSizeBytes

B TableSize

C TotalTableSizeBytes

D SizeBytes

💡 Hint

Look for the exact metric name used by AWS CloudWatch for table size.

The correct metric name is TableSizeBytes, which reports the total size of the table in bytes.

❓ optimization

advanced

Optimizing DynamoDB Table Performance Using CloudWatch Metrics

You notice that the ConsumedReadCapacityUnits metric is consistently close to the provisioned read capacity, and ReadThrottleEvents occasionally spikes. What is the best action to reduce throttling?

A Decrease the provisioned read capacity units to save cost.

B Switch to eventually consistent reads to reduce read capacity usage.

C Disable CloudWatch monitoring to reduce overhead.

D Increase the provisioned read capacity units for the table.

💡 Hint

Think about how to handle capacity limits and throttling.

Increasing provisioned read capacity units allows more read requests per second, reducing throttling.

🔧 Debug

expert

Diagnosing Unexpected High Write Capacity Consumption

A DynamoDB table shows unexpectedly high ConsumedWriteCapacityUnits in CloudWatch, but your application writes are low. Which of the following is the most likely cause?

A A large number of small write requests causing inefficient capacity usage.

B The table is being read heavily, causing write capacity to spike.

C The table's read capacity units are being consumed instead.

D CloudWatch metrics are delayed and not accurate.

💡 Hint

Consider how write request size affects capacity consumption.

Many small writes consume more write capacity units inefficiently, causing high ConsumedWriteCapacityUnits despite low write count.

Practice

1. What does the CloudWatch metric ConsumedReadCapacityUnits for a DynamoDB table represent?

easy

A. The number of read capacity units consumed by the table over a period

B. The total number of items in the table

C. The amount of storage used by the table

D. The number of write capacity units consumed by the table over a period

Solution

1. Step 1: Understand the metric name

   ConsumedReadCapacityUnits clearly indicates it measures read capacity units consumed.

2. Step 2: Relate to DynamoDB usage

   Read capacity units measure how many read operations the table performs, so this metric tracks usage over time.

3. Final Answer:

   The number of read capacity units consumed by the table over a period -> Option A

4. Quick Check:

   ConsumedReadCapacityUnits = Read usage [OK]

Hint: Look for 'Read' in metric name to identify read capacity usage [OK]

Common Mistakes:

• Confusing read capacity with write capacity
• Thinking it measures item count or storage size
• Assuming it shows total capacity, not consumed

2. Which AWS CLI command syntax correctly retrieves the ThrottledRequests metric for a DynamoDB table named Orders?

easy

A. aws cloudwatch list-metrics --metric ThrottledRequests --table Orders

B. aws cloudwatch get-metric-statistics --metric-name ThrottledRequests --namespace AWS/DynamoDB --dimensions Name=TableName,Value=Orders --start-time 2024-01-01T00:00:00Z --end-time 2024-01-01T01:00:00Z --period 60 --statistics Sum

C. aws cloudwatch describe-metrics --metric-name ThrottledRequests --table Orders

D. aws dynamodb get-metric --metric ThrottledRequests --table Orders

Solution

1. Step 1: Identify correct AWS CLI service and command

   CloudWatch metrics use aws cloudwatch get-metric-statistics to retrieve metric data.

2. Step 2: Check parameters for metric retrieval

   aws cloudwatch get-metric-statistics --metric-name ThrottledRequests --namespace AWS/DynamoDB --dimensions Name=TableName,Value=Orders --start-time 2024-01-01T00:00:00Z --end-time 2024-01-01T01:00:00Z --period 60 --statistics Sum correctly specifies metric name, namespace, dimensions (table name), time range, period, and statistics.

3. Final Answer:

   aws cloudwatch get-metric-statistics with correct parameters -> Option B

4. Quick Check:

   Use aws cloudwatch get-metric-statistics for metrics [OK]

Hint: Use 'aws cloudwatch get-metric-statistics' with proper parameters [OK]

Common Mistakes:

• Using 'aws dynamodb' instead of 'aws cloudwatch'
• Missing required parameters like dimensions or time range
• Using commands that only list or describe metrics, not retrieve data

3. Given the following AWS CLI command output snippet for ConsumedWriteCapacityUnits metric of a DynamoDB table:

{"Datapoints": [{"Timestamp": "2024-06-01T12:00:00Z", "Sum": 150}], "Label": "ConsumedWriteCapacityUnits"}

What does the value 150 represent?

medium

A. The maximum write capacity units allowed for the table

B. The average number of write capacity units available

C. The number of throttled write requests

D. The total number of write capacity units consumed during the specified period

Solution

1. Step 1: Understand the metric and statistic

   The metric is ConsumedWriteCapacityUnits and the statistic is Sum, meaning total units consumed.

2. Step 2: Interpret the value 150

   150 is the sum of write capacity units consumed during the time period ending at the timestamp.

3. Final Answer:

   The total number of write capacity units consumed during the specified period -> Option D

4. Quick Check:

   Sum of consumed write units = 150 [OK]

Hint: Sum statistic means total units consumed, not average or max [OK]

Common Mistakes:

• Confusing sum with average or max
• Thinking it shows capacity limits instead of usage
• Mixing write capacity with throttled requests

4. You wrote this AWS CLI command to get the ReadThrottleEvents metric for your DynamoDB table Users but got an error:

aws cloudwatch get-metric-statistics --metric-name ReadThrottleEvents --namespace AWS/DynamoDB --dimensions TableName=Users --start-time 2024-06-01T00:00:00Z --end-time 2024-06-01T01:00:00Z --period 60 --statistics Sum

What is the error and how do you fix it?

medium

A. The period value is too small; increase it to 300

B. The metric name is invalid; use ThrottledRequests instead

C. The dimension syntax is incorrect; use --dimensions Name=TableName,Value=Users

D. The start-time format is wrong; use MM-DD-YYYY

Solution

1. Step 1: Check dimension syntax in AWS CLI

   The correct syntax for dimensions is --dimensions Name=TableName,Value=Users, not just TableName=Users.

2. Step 2: Fix the command by correcting dimensions

   Replace --dimensions TableName=Users with --dimensions Name=TableName,Value=Users to fix the error.

3. Final Answer:

   The dimension syntax is incorrect; use --dimensions Name=TableName,Value=Users -> Option C

4. Quick Check:

   Dimensions need Name and Value keys [OK]

Hint: Dimensions require Name= and Value= pairs in AWS CLI [OK]

Common Mistakes:

• Using incorrect dimension syntax without Name= and Value=
• Confusing metric names that don't exist
• Incorrect date/time format for start-time

5. You want to monitor your DynamoDB table's performance and set an alarm if the ThrottledRequests metric exceeds 5 in any 5-minute period. Which combination of CloudWatch metric and alarm configuration is correct?

hard

A. Use metric ThrottledRequests with statistic Sum over 300 seconds period, alarm threshold > 5

B. Use metric ConsumedReadCapacityUnits with statistic Average over 60 seconds period, alarm threshold > 5

C. Use metric ThrottledRequests with statistic Maximum over 60 seconds period, alarm threshold > 5

D. Use metric ReadThrottleEvents with statistic Sum over 300 seconds period, alarm threshold > 10

Solution

1. Step 1: Identify correct metric for throttled requests

   The metric ThrottledRequests tracks throttling events, so it is the right choice.

2. Step 2: Choose appropriate statistic and period

   Sum over 300 seconds (5 minutes) aggregates total throttled requests in that period, matching the alarm condition.

3. Step 3: Set alarm threshold correctly

   Alarm triggers if sum exceeds 5, matching the requirement.

4. Final Answer:

   Use metric ThrottledRequests with statistic Sum over 300 seconds period, alarm threshold > 5 -> Option A

5. Quick Check:

   Sum over 5 minutes > 5 throttled requests triggers alarm [OK]

Hint: Sum metric over 5 minutes matches throttled requests count [OK]

Common Mistakes:

• Using wrong metric like ConsumedReadCapacityUnits
• Choosing Average or Maximum instead of Sum for count
• Setting period too short to capture throttling spikes