Event-driven architecture patterns in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Querying DynamoDB Stream Events for Specific Event Types

You have a DynamoDB table with streams enabled. The stream records include events of types INSERT, MODIFY, and REMOVE. Which query expression will correctly filter and return only the INSERT events from the stream records?

DynamoDB

SELECT * FROM StreamRecords WHERE eventName = 'INSERT';

A SELECT * FROM StreamRecords WHERE eventName = 'ADD';

B SELECT * FROM StreamRecords WHERE eventType = 'INSERT';

C SELECT * FROM StreamRecords WHERE eventName = 'INSERT';

D SELECT * FROM StreamRecords WHERE eventName = 'CREATE';

💡 Hint

Check the exact attribute name used for event type in DynamoDB streams.

DynamoDB stream records use the attribute 'eventName' to indicate the type of event, such as INSERT, MODIFY, or REMOVE. Using 'eventName = 'INSERT'' correctly filters for insert events.

🧠 Conceptual

intermediate

Understanding Event Sourcing with DynamoDB

In an event-driven architecture using DynamoDB, what is the main advantage of using event sourcing to store changes as events rather than storing only the current state?

A It allows reconstructing the entire state history by replaying events.

B It reduces the storage size by storing only the latest state.

C It eliminates the need for DynamoDB streams.

D It automatically indexes all events for faster queries.

💡 Hint

Think about how event sourcing helps with state recovery and auditing.

Event sourcing stores all changes as events, enabling the system to rebuild the current state by replaying these events. This provides a full history and audit trail.

📝 Syntax

advanced

Correct Syntax for DynamoDB Stream Event Processing in Lambda

Which of the following AWS Lambda event handler code snippets correctly accesses the new image of a DynamoDB stream record for an INSERT event?

DynamoDB

exports.handler = async (event) => {
  for (const record of event.Records) {
    if (record.eventName === 'INSERT') {
      const newImage = record.dynamodb.NewImage;
      // process newImage
    }
  }
};

A const newImage = record.dynamodb.NewImage;

B const newImage = record.dynamodb.newImage;

C const newImage = record.DynamoDB.NewImage;

D const newImage = record.dynamodb.OldImage;

💡 Hint

Check the exact casing and property names in the DynamoDB stream record object.

The correct property to access the new image is 'NewImage' under 'dynamodb' in the stream record. It is case-sensitive.

❓ optimization

advanced

Optimizing Event Processing with DynamoDB Streams and Lambda

You want to optimize your Lambda function triggered by DynamoDB streams to process events efficiently. Which approach will best reduce cold start latency and improve throughput?

A Set the batch size to 1 to process events one by one for simplicity.

B Use batch processing by setting the batch size to a higher number in the event source mapping.

C Disable parallelization to ensure events are processed sequentially.

D Increase the Lambda timeout to the maximum allowed to avoid timeouts.

💡 Hint

Think about how batch size affects invocation frequency and processing speed.

Increasing batch size allows Lambda to process multiple records in one invocation, reducing overhead and cold starts, thus improving throughput.

🔧 Debug

expert

Debugging Missing Events in DynamoDB Stream Processing

Your Lambda function processing DynamoDB stream events sometimes misses INSERT events. Which of the following is the most likely cause?

A The Lambda function code incorrectly accesses 'OldImage' instead of 'NewImage'.

B The DynamoDB table does not have streams enabled.

C The Lambda event source mapping has a filter that excludes INSERT events.

D The DynamoDB stream is set to KEYS_ONLY, so new images are not available.

💡 Hint

Consider the stream view type configuration and what data it provides.

If the stream is set to KEYS_ONLY, only keys are included in stream records, so the Lambda cannot access the full new image of inserted items, causing missing event data.

Practice

1. What is the main purpose of using DynamoDB Streams in an event-driven architecture?

easy

A. To capture and record changes in the DynamoDB table as events

B. To store backup copies of the DynamoDB table

C. To increase the read capacity of the DynamoDB table

D. To encrypt data stored in DynamoDB

Solution

1. Step 1: Understand DynamoDB Streams role

   DynamoDB Streams capture data modification events like inserts, updates, and deletes.

2. Step 2: Identify the purpose in event-driven architecture

   These captured events trigger other processes automatically, enabling real-time reactions.

3. Final Answer:

   To capture and record changes in the DynamoDB table as events -> Option A

4. Quick Check:

   DynamoDB Streams = capture changes [OK]

Hint: Streams capture table changes as events for triggers [OK]

Common Mistakes:

• Confusing Streams with backups
• Thinking Streams increase capacity
• Assuming Streams encrypt data

2. Which of the following is the correct way to enable DynamoDB Streams on a table using AWS CLI?

easy

A. aws dynamodb set-stream --table MyTable --enabled true

B. aws dynamodb enable-stream --table MyTable --type NEW_IMAGE

C. aws dynamodb create-stream --table-name MyTable --view-type KEYS_ONLY

D. aws dynamodb update-table --table-name MyTable --stream-specification StreamEnabled=true,StreamViewType=NEW_AND_OLD_IMAGES

Solution

1. Step 1: Recall AWS CLI command for enabling streams

   The correct command uses 'update-table' with '--stream-specification' to enable streams.

2. Step 2: Verify syntax and parameters

   aws dynamodb update-table --table-name MyTable --stream-specification StreamEnabled=true,StreamViewType=NEW_AND_OLD_IMAGES correctly sets StreamEnabled=true and specifies StreamViewType as NEW_AND_OLD_IMAGES.

3. Final Answer:

   aws dynamodb update-table --table-name MyTable --stream-specification StreamEnabled=true,StreamViewType=NEW_AND_OLD_IMAGES -> Option D

4. Quick Check:

   Enable streams = update-table + stream-specification [OK]

Hint: Use update-table with stream-specification to enable streams [OK]

Common Mistakes:

• Using non-existent commands like enable-stream
• Incorrect parameter names
• Confusing create-stream with enabling streams

3. Given a DynamoDB Stream enabled with StreamViewType=NEW_IMAGE, what will an AWS Lambda function receive when an item is updated?

medium

A. Only the keys of the updated item

B. The entire item before and after the update

C. Only the new version of the item after the update

D. No data, only a notification that an update occurred

Solution

1. Step 1: Understand StreamViewType NEW_IMAGE meaning

   NEW_IMAGE sends only the new version of the item after the change.

2. Step 2: Determine what Lambda receives on update

   Lambda gets the updated item data, not the old version or just keys.

3. Final Answer:

   Only the new version of the item after the update -> Option C

4. Quick Check:

   NEW_IMAGE = new item data only [OK]

Hint: NEW_IMAGE sends only updated item data to Lambda [OK]

Common Mistakes:

• Confusing NEW_IMAGE with NEW_AND_OLD_IMAGES
• Assuming keys only are sent
• Thinking Lambda gets no data

4. You wrote a Lambda function triggered by DynamoDB Streams but it never executes. What is the most likely cause?

medium

A. The DynamoDB table does not have Streams enabled

B. The Lambda function is not subscribed to the stream

C. The Lambda function code has syntax errors

D. The DynamoDB table has no data

Solution

1. Step 1: Check if Streams are enabled

   If Streams were not enabled, no events would be generated, but question implies setup.

2. Step 2: Verify Lambda subscription to the stream

   Without subscribing Lambda to the stream, it won't trigger on events.

3. Final Answer:

   The Lambda function is not subscribed to the stream -> Option B

4. Quick Check:

   Lambda must be subscribed to stream to trigger [OK]

Hint: Ensure Lambda is subscribed to DynamoDB Stream [OK]

Common Mistakes:

• Assuming syntax errors stop invocation
• Thinking empty table stops Lambda trigger
• Ignoring subscription setup

5. You want to build a real-time notification system using DynamoDB and Lambda. Which event-driven architecture pattern best fits this use case?

hard

A. Use DynamoDB Streams to capture changes and trigger Lambda to send notifications

B. Use periodic polling of DynamoDB to check for changes and send notifications

C. Use DynamoDB Global Tables to replicate data and notify users

D. Use DynamoDB backups to trigger notifications on data changes

Solution

1. Step 1: Identify real-time event-driven pattern

   Real-time notifications require immediate reaction to data changes.

2. Step 2: Match pattern with DynamoDB Streams and Lambda

   Streams capture changes as events; Lambda processes them instantly to notify users.

3. Final Answer:

   Use DynamoDB Streams to capture changes and trigger Lambda to send notifications -> Option A

4. Quick Check:

   Streams + Lambda = real-time notifications [OK]

Hint: Streams trigger Lambda for instant notifications [OK]

Common Mistakes:

• Choosing polling which is not real-time
• Confusing replication with notifications
• Using backups which are not event triggers