DynamoDB Streams overview in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does DynamoDB Streams capture data changes?

Which statement best describes how DynamoDB Streams captures changes in a DynamoDB table?

A It sends notifications to an email address for each data change.

B It captures only the final state of the table once every hour.

C It stores a backup of the entire table every time a change happens.

D It records every data modification as a stream record in the order they occurred.

💡 Hint

Think about how a stream works as a sequence of events.

DynamoDB Streams records each data modification as a stream record in the order they occur, allowing applications to process changes sequentially.

❓ service_behavior

intermediate

What happens when you enable DynamoDB Streams on a table?

After enabling DynamoDB Streams on a table, what is the immediate effect on the table's behavior?

A The table sends a summary report of changes to CloudWatch Logs.

B The table starts recording item-level changes as stream records for up to 24 hours.

C The table disables all write operations until the stream is processed.

D The table automatically backs up all data to S3 every 5 minutes.

💡 Hint

Consider what DynamoDB Streams stores and for how long.

When enabled, DynamoDB Streams records item-level changes as stream records and retains them for 24 hours for processing.

❓ Architecture

advanced

Designing a system to process DynamoDB Streams with Lambda

You want to process DynamoDB Streams records using AWS Lambda. Which architecture ensures that each stream record is processed exactly once and in order?

A Configure Lambda with batch size 1 and enable the 'bisect on function error' option.

B Use multiple Lambda functions triggered by the same stream to increase parallelism.

C Set Lambda batch size to maximum and disable retries to speed up processing.

D Process the stream records manually by polling the stream with a custom script.

💡 Hint

Think about how to maintain order and avoid duplicate processing.

Setting batch size to 1 and enabling 'bisect on function error' helps Lambda process each record exactly once and in order, handling errors gracefully.

❓ security

advanced

Securing access to DynamoDB Streams

Which IAM policy action is required to allow a Lambda function to read from a DynamoDB Stream?

A "lambda:InvokeFunction" and "dynamodb:DeleteStream"

B "dynamodb:PutItem" and "dynamodb:UpdateItem"

C "dynamodb:DescribeStream" and "dynamodb:GetRecords"

D "s3:GetObject" and "dynamodb:Scan"

💡 Hint

Focus on permissions related to reading stream data.

To read from DynamoDB Streams, the Lambda function needs permissions like "dynamodb:DescribeStream" and "dynamodb:GetRecords" to access stream details and records.

✅ Best Practice

expert

Handling stream record retention and data loss risks

DynamoDB Streams retains records for 24 hours. What is the best practice to avoid data loss if your stream processing application is down for longer than 24 hours?

A Use DynamoDB Streams with Kinesis Data Streams to extend retention and replay capability.

B Increase the stream retention period to 7 days in the DynamoDB table settings.

C Periodically back up the DynamoDB table and restore it if the stream is lost.

D Implement a dead-letter queue (DLQ) to capture failed stream records for later processing.

💡 Hint

Consider how to extend stream retention beyond the default limit.

DynamoDB Streams retention is fixed at 24 hours. Integrating with Kinesis Data Streams allows longer retention and replay, preventing data loss during downtime.

Practice

1. What is the main purpose of DynamoDB Streams?

easy

A. To store backups of DynamoDB tables permanently

B. To encrypt data stored in DynamoDB tables

C. To increase the read capacity of a DynamoDB table

D. To track and react to data changes in real time

Solution

1. Step 1: Understand DynamoDB Streams function

   DynamoDB Streams capture data changes like inserts, updates, and deletes in real time.

2. Step 2: Compare options with Streams purpose

   Only To track and react to data changes in real time correctly describes tracking and reacting to data changes. Other options describe unrelated features.

3. Final Answer:

   To track and react to data changes in real time -> Option D

4. Quick Check:

   DynamoDB Streams = Track data changes [OK]

Hint: Streams capture table changes instantly for reaction [OK]

Common Mistakes:

• Confusing Streams with backup or encryption features
• Thinking Streams increase read capacity
• Assuming Streams store data permanently

2. Which setting must be enabled to start using DynamoDB Streams on a table?

easy

A. EncryptionEnabled set to true

B. BackupEnabled set to true

C. StreamEnabled set to true

D. AutoScalingEnabled set to true

Solution

1. Step 1: Identify the configuration for enabling Streams

   To use DynamoDB Streams, the table must have StreamEnabled set to true.

2. Step 2: Eliminate unrelated settings

   BackupEnabled, EncryptionEnabled, and AutoScalingEnabled do not enable Streams.

3. Final Answer:

   StreamEnabled set to true -> Option C

4. Quick Check:

   Enable Streams = StreamEnabled true [OK]

Hint: Enable Streams by setting StreamEnabled true [OK]

Common Mistakes:

• Confusing Streams with backups or encryption
• Assuming AutoScaling enables Streams
• Forgetting to enable Streams explicitly

3. Given a DynamoDB Stream with StreamViewType set to NEW_AND_OLD_IMAGES, what data will the stream record for each change?

medium

A. Only the new item image after the change

B. Both the new and old item images

C. Only the keys of the changed items

D. Only the old item image before the change

Solution

1. Step 1: Understand StreamViewType NEW_AND_OLD_IMAGES meaning

   This setting records both the item before and after the change.

2. Step 2: Compare options with StreamViewType behavior

   Only Both the new and old item images matches the behavior of capturing both new and old images.

3. Final Answer:

   Both the new and old item images -> Option B

4. Quick Check:

   NEW_AND_OLD_IMAGES = new + old data [OK]

Hint: NEW_AND_OLD_IMAGES means capture before and after data [OK]

Common Mistakes:

• Choosing only new or only old images
• Confusing keys only with full images
• Not knowing StreamViewType options

4. A developer enabled DynamoDB Streams but does not see any stream records after table updates. What is the most likely cause?

medium

A. StreamEnabled is false on the table

B. StreamViewType is set to KEYS_ONLY

C. Stream retention period is set to 7 days

D. The table has no primary key defined

Solution

1. Step 1: Check if Streams are enabled

   If StreamEnabled is false, no stream records are generated regardless of updates.

2. Step 2: Evaluate other options

   KEYS_ONLY still produces records; retention period (24-168 hours) does not prevent seeing recent records; tables require primary keys but that doesn't stop streams if enabled.

3. Final Answer:

   StreamEnabled is false on the table -> Option A

4. Quick Check:

   No records = Streams not enabled [OK]

Hint: Streams must be enabled to see records [OK]

Common Mistakes:

• Assuming KEYS_ONLY disables records
• Thinking retention period prevents seeing records
• Ignoring StreamEnabled setting

5. You want to trigger a Lambda function whenever an item is updated in your DynamoDB table to process both the old and new item images. Which DynamoDB Streams configuration and setup is required?

hard

A. Enable Streams with StreamViewType NEW_AND_OLD_IMAGES and configure Lambda trigger on the stream

B. Enable Streams with StreamViewType KEYS_ONLY and configure Lambda trigger on the table

C. Enable Streams with StreamViewType NEW_IMAGE and configure Lambda trigger on the stream

D. Enable Streams with StreamViewType OLD_IMAGE and configure Lambda trigger on the table

Solution

1. Step 1: Choose StreamViewType for updates

   To capture both before and after update data, use NEW_AND_OLD_IMAGES.

2. Step 2: Configure Lambda trigger on the DynamoDB Stream

   Lambda triggers must be set on the stream, not directly on the table.

3. Final Answer:

   Enable Streams with StreamViewType NEW_AND_OLD_IMAGES and configure Lambda trigger on the stream -> Option A

4. Quick Check:

   Lambda trigger on stream with NEW_AND_OLD_IMAGES [OK]

Hint: Use NEW_AND_OLD_IMAGES and trigger Lambda on stream [OK]

Common Mistakes:

• Triggering Lambda directly on table instead of stream
• Choosing KEYS_ONLY or OLD_IMAGE for update data
• Not enabling Streams before Lambda trigger