Lambda trigger on stream events in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the event source for the Lambda trigger.

DynamoDB

EventSourceArn: [1]

Drag options to blanks, or click blank then click option'

Aarn:aws:sqs:region:account-id:queue_name

Barn:aws:s3:::bucket_name

Carn:aws:dynamodb:region:account-id:table/TableName/stream/label

Darn:aws:lambda:region:account-id:function:FunctionName

Attempts:

3 left

💡 Hint

Common Mistakes

Using an S3 bucket ARN instead of a DynamoDB stream ARN.

Using the Lambda function ARN as the event source.

Using an SQS queue ARN instead of a DynamoDB stream ARN.

The event source ARN must point to the DynamoDB stream ARN to trigger the Lambda on stream events.

2fill in blank

medium

Complete the code to specify the batch size for the Lambda event source mapping.

DynamoDB

BatchSize: [1]

Drag options to blanks, or click blank then click option'

A10

B100

C1000

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Setting batch size too high causing timeouts.

Setting batch size too low causing inefficient processing.

The batch size defines how many records the Lambda function receives in one batch. 100 is a common default for DynamoDB streams.

3fill in blank

hard

Fix the error in the code to enable the Lambda trigger on the DynamoDB stream.

DynamoDB

StartingPosition: [1]

Drag options to blanks, or click blank then click option'

ATRIM_HORIZON

BBEGINNING

CLATEST

DEARLIEST

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'BEGINNING' or 'EARLIEST' which are invalid for DynamoDB streams.

Using 'LATEST' when you want to process all existing records.

The correct starting position for DynamoDB streams is 'TRIM_HORIZON' to start from the oldest available record.

4fill in blank

hard

Fill both blanks to create a Lambda event source mapping with enabled status and correct batch size.

DynamoDB

EventSourceArn: [1], BatchSize: [2]

Drag options to blanks, or click blank then click option'

Aarn:aws:dynamodb:region:account-id:table/TableName/stream/label

B50

C100

Darn:aws:s3:::bucket_name

Attempts:

3 left

💡 Hint

Common Mistakes

Using an S3 ARN instead of DynamoDB stream ARN.

Choosing batch size too small or too large.

The event source ARN must be the DynamoDB stream ARN and batch size 100 is a good choice for processing.

5fill in blank

hard

Fill all three blanks to configure a Lambda trigger with event source ARN, batch size, and starting position.

DynamoDB

EventSourceArn: [1], BatchSize: [2], StartingPosition: [3]

Drag options to blanks, or click blank then click option'

Aarn:aws:dynamodb:region:account-id:table/TableName/stream/label

B100

CTRIM_HORIZON

DLATEST

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'LATEST' as starting position when wanting to process all records.

Using incorrect ARN or batch size.

Use the DynamoDB stream ARN, batch size 100, and starting position 'TRIM_HORIZON' to process all stream records from the beginning.

Practice

1. What is the main purpose of a Lambda trigger on DynamoDB stream events?

easy

A. To backup the DynamoDB table data to S3

B. To manually update the DynamoDB table from the Lambda console

C. To disable the DynamoDB stream temporarily

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

Solution

1. Step 1: Understand DynamoDB streams

   DynamoDB streams capture data changes like inserts, updates, and deletes.

2. Step 2: Role of Lambda triggers

   Lambda triggers run code automatically when these stream events occur.

3. Final Answer:

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

4. Quick Check:

   Lambda triggers = auto-run code on data change [OK]

Hint: Lambda triggers run code automatically on data changes [OK]

Common Mistakes:

• Thinking Lambda triggers require manual execution
• Confusing stream enabling with backup
• Assuming Lambda disables streams

2. Which of the following is the correct way to specify a Lambda trigger for a DynamoDB stream in AWS Console?

easy

A. Enable stream on the table, then add Lambda as a trigger on the stream

B. Create Lambda function first, then enable stream on the table

C. Enable stream on the table and Lambda separately without linking

D. Add Lambda trigger before enabling the stream on the table

Solution

1. Step 1: Enable stream on DynamoDB table

   Streams must be enabled first to capture data changes.

2. Step 2: Add Lambda as a trigger on the enabled stream

   Lambda triggers are linked to the stream to react to events.

3. Final Answer:

   Enable stream on the table, then add Lambda as a trigger on the stream -> Option A

4. Quick Check:

   Enable stream first, then add Lambda trigger [OK]

Hint: Enable stream first, then attach Lambda trigger [OK]

Common Mistakes:

• Trying to add Lambda trigger before enabling stream
• Not linking Lambda to the stream
• Enabling stream and Lambda separately without connection

3. Given this Lambda function snippet triggered by a DynamoDB stream event:

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

What will this code output when a new item with id '123' is inserted?

medium

A. It prints '123' to the logs

B. It prints the old image of the item

C. It raises a KeyError because 'NewImage' is missing

D. It prints nothing because eventName is 'MODIFY'

Solution

1. Step 1: Check eventName condition

   The code checks if eventName is 'INSERT', which matches new item insertion.

2. Step 2: Access NewImage id value

   It accesses 'NewImage' dictionary and prints the 'id' string value '123'.

3. Final Answer:

   It prints '123' to the logs -> Option A

4. Quick Check:

   INSERT event prints new id '123' [OK]

Hint: INSERT event uses NewImage to get new item data [OK]

Common Mistakes:

• Confusing NewImage with OldImage
• Assuming eventName is MODIFY instead of INSERT
• Not accessing nested dictionary keys correctly

4. You wrote this Lambda code to process DynamoDB stream events but it throws a runtime error:

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

What is the likely cause of the error?

medium

A. The 'id' attribute is always an integer, not a string

B. The event may contain DELETE events without NewImage data

C. The event['Records'] key is missing

D. Lambda functions cannot access DynamoDB streams

Solution

1. Step 1: Understand stream event types

   DELETE events do not have 'NewImage', only 'OldImage'.

2. Step 2: Accessing NewImage without check causes error

   Trying to access 'NewImage' on DELETE events causes a KeyError.

3. Final Answer:

   The event may contain DELETE events without NewImage data -> Option B

4. Quick Check:

   DELETE events lack NewImage causing runtime error [OK]

Hint: Check event type before accessing NewImage [OK]

Common Mistakes:

• Assuming all events have NewImage
• Ignoring DELETE event structure
• Believing Lambda can't access streams

5. You want your Lambda triggered by DynamoDB streams to process only UPDATE events where the attribute 'status' changed to 'completed'. Which approach is best?

hard

A. Filter events in DynamoDB stream settings to only send UPDATE events with 'completed' status

B. Use a separate Lambda for each event type and status value

C. In Lambda, check if eventName is 'MODIFY' and compare OldImage and NewImage 'status' values

D. Enable stream with only KEYS_ONLY to reduce data size

Solution

1. Step 1: Understand stream filtering limits

   DynamoDB streams cannot filter by attribute values, only event types.

2. Step 2: Use Lambda code to check eventName and compare status

   Lambda can check if eventName is 'MODIFY' and compare OldImage and NewImage 'status' to detect change to 'completed'.

3. Final Answer:

   In Lambda, check if eventName is 'MODIFY' and compare OldImage and NewImage 'status' values -> Option C

4. Quick Check:

   Filter in Lambda by event and attribute change [OK]

Hint: Filter attribute changes inside Lambda, not in stream settings [OK]

Common Mistakes:

• Trying to filter by attribute in stream settings
• Using KEYS_ONLY which lacks attribute data
• Creating multiple Lambdas unnecessarily