Lambda with DynamoDB Streams in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is AWS Lambda in simple terms?

AWS Lambda is a service that runs your code automatically when something happens, without you needing to manage servers.

beginner

What is DynamoDB Streams?

DynamoDB Streams captures changes (like adds, updates, deletes) in a DynamoDB table and lets other services react to those changes.

intermediate

How does Lambda work with DynamoDB Streams?

Lambda listens to the stream of changes from DynamoDB and runs your code automatically for each change, like a helper reacting to updates.

intermediate

Why use Lambda with DynamoDB Streams?

It helps automate tasks like sending notifications or updating other systems whenever your database changes, without manual work.

advanced

What is a best practice when configuring Lambda with DynamoDB Streams?

Set the batch size to control how many records Lambda processes at once and handle errors to avoid losing data.

What triggers an AWS Lambda function when using DynamoDB Streams?

A Changes in the DynamoDB table

B Manual button press

C Scheduled time only

D User login event

Lambda is triggered automatically by changes (inserts, updates, deletes) in the DynamoDB table via Streams.

What type of data does DynamoDB Streams provide to Lambda?

A User credentials

B Full database backup

C A list of changed records

D Server logs

DynamoDB Streams sends a list of records that changed, so Lambda can process each change.

Which Lambda setting controls how many stream records are processed at once?

A Timeout

B Batch size

C Memory size

D Runtime version

Batch size defines how many records Lambda reads from the stream in one go.

What happens if Lambda fails to process a DynamoDB Stream record?

A The database rolls back changes

B The record is deleted immediately

C Lambda shuts down permanently

D The record can be retried or sent to a dead-letter queue

Failed records can be retried or sent to a dead-letter queue for later inspection.

Why is using Lambda with DynamoDB Streams considered event-driven architecture?

A Because Lambda reacts automatically to database events

B Because it uses scheduled tasks

C Because it requires manual triggers

D Because it stores data permanently

Event-driven means actions happen automatically when events (like data changes) occur.

Explain how AWS Lambda and DynamoDB Streams work together to automate tasks.

Think about how a helper reacts when something changes in your database.

Describe best practices for configuring Lambda functions that process DynamoDB Streams.

Consider how to keep your automation reliable and efficient.

Practice

1. What is the main purpose of connecting AWS Lambda to DynamoDB Streams?

easy

A. To manually trigger Lambda functions from the AWS console

B. To automatically run code when data in the DynamoDB table changes

C. To backup DynamoDB data to S3 automatically

D. To increase the read capacity of the DynamoDB table

Solution

1. Step 1: Understand DynamoDB Streams role

   DynamoDB Streams capture data changes in the table as events.

2. Step 2: Understand Lambda integration

   Lambda can be triggered automatically by these stream events to run code.

3. Final Answer:

   To automatically run code when data in the DynamoDB table changes -> Option B

4. Quick Check:

   Lambda triggers on stream events = A [OK]

Hint: Streams trigger Lambda on data changes automatically [OK]

Common Mistakes:

• Thinking Lambda triggers manually from console
• Confusing streams with backups
• Assuming streams increase table capacity

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

easy

A. Create a Lambda function and attach it to the table

B. Enable versioning on the DynamoDB table

C. Set the stream specification to NEW_AND_OLD_IMAGES in the table settings

D. Increase the write capacity units of the table

Solution

1. Step 1: Identify how to enable streams

   DynamoDB Streams are enabled by setting the stream specification on the table.

2. Step 2: Choose correct stream view type

   NEW_AND_OLD_IMAGES captures both before and after images of changes.

3. Final Answer:

   Set the stream specification to NEW_AND_OLD_IMAGES in the table settings -> Option C

4. Quick Check:

   Stream enabled via table settings = B [OK]

Hint: Enable streams in table settings, not in Lambda [OK]

Common Mistakes:

• Trying to enable streams by creating Lambda
• Confusing versioning with streams
• Changing capacity units instead of streams

3. Given this Lambda event handler code snippet triggered by DynamoDB Streams:

def lambda_handler(event, context):
    for record in event['Records']:
        if record['eventName'] == 'INSERT':
            print(record['dynamodb']['NewImage']['id']['S'])

What will this code print when a new item with id '123' is added to the DynamoDB table?

medium

A. '123' printed once for the new item

B. 'id' key printed instead of its value

C. An error because 'NewImage' does not exist

D. Nothing, because eventName is not 'INSERT'

Solution

1. Step 1: Understand event structure for INSERT

   For an INSERT event, 'NewImage' contains the new item data including 'id'.

2. Step 2: Analyze code behavior

   The code prints the string value of 'id' from 'NewImage' when eventName is 'INSERT'.

3. Final Answer:

   '123' printed once for the new item -> Option A

4. Quick Check:

   INSERT event prints new id value = D [OK]

Hint: INSERT events have NewImage with new item data [OK]

Common Mistakes:

• Assuming eventName is different
• Expecting OldImage on INSERT
• Confusing key name with value

4. You deployed a Lambda function triggered by DynamoDB Streams but it never runs. Which of the following is the most likely cause?

medium

A. The DynamoDB table does not have streams enabled

B. The Lambda function code has a syntax error

C. The DynamoDB table has no read capacity units

D. The Lambda function has no execution role

Solution

1. Step 1: Check stream enablement

   Lambda triggers on DynamoDB Streams events, so streams must be enabled on the table.

2. Step 2: Consider other causes

   While code errors or roles cause failures, the function would still be invoked if streams exist.

3. Final Answer:

   The DynamoDB table does not have streams enabled -> Option A

4. Quick Check:

   Streams must be enabled for Lambda trigger = C [OK]

Hint: Check if streams are enabled on the table first [OK]

Common Mistakes:

• Assuming code errors prevent invocation
• Ignoring missing streams
• Confusing read capacity with triggers

5. You want your Lambda function to process only updated attributes from DynamoDB Streams and ignore inserts and deletes. Which stream view type and event filter should you use?

hard

A. Enable NEW_AND_OLD_IMAGES stream view and filter events where eventName is 'INSERT'

B. Enable KEYS_ONLY stream view and filter events where eventName is 'INSERT'

C. Enable OLD_IMAGE stream view and filter events where eventName is 'REMOVE'

D. Enable NEW_IMAGE stream view and filter events where eventName is 'MODIFY'

Solution

1. Step 1: Choose stream view for updated data

   NEW_IMAGE provides the new state after update, suitable for processing changes.

2. Step 2: Filter events for updates only

   Filtering on eventName 'MODIFY' ensures only update events trigger Lambda.

3. Final Answer:

   Enable NEW_IMAGE stream view and filter events where eventName is 'MODIFY' -> Option D

4. Quick Check:

   Updates = NEW_IMAGE + 'MODIFY' filter [OK]

Hint: Use NEW_IMAGE and 'MODIFY' event filter for updates only [OK]

Common Mistakes:

• Using KEYS_ONLY which lacks attribute data
• Filtering on INSERT or REMOVE instead of MODIFY
• Choosing OLD_IMAGE which shows old data only