Event triggers for Lambda in AWS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the AWS service that triggers the Lambda function.

AWS

Event source for Lambda is [1].

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

ARDS

BEC2

CVPC

DS3

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing EC2 which is a compute service, not an event source for Lambda.

S3 is a common event source that triggers Lambda functions when objects are created or deleted.

2fill in blank

medium

Complete the code to specify the event type that triggers Lambda on S3.

AWS

Lambda triggers on S3 event type: [1].

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

ADBUpdate

BInstanceStart

CObjectCreated

DNetworkChange

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting unrelated event types like 'InstanceStart' which is for EC2.

The 'ObjectCreated' event triggers Lambda when a new object is added to an S3 bucket.

3fill in blank

hard

Fix the error in the event source mapping code for Lambda trigger.

AWS

Event source mapping: {
  "EventSourceArn": "arn:aws:sqs:us-east-1:123456789012:MyQueue",
  "FunctionName": "MyLambdaFunction",
  "[1]": true
}

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

AEnable

BEnabled

CActive

DStatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Enable' which is incorrect property name.

The correct property to enable the event source mapping is 'Enabled'.

4fill in blank

hard

Fill both blanks to configure a CloudWatch event rule to trigger Lambda every 5 minutes.

AWS

Rule = {
  "ScheduleExpression": "[1]",
  "Targets": [{"Arn": "arn:aws:lambda:us-east-1:123456789012:function:MyFunction", "Id": "[2]"}]
}

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

Arate(5 minutes)

Bcron(0/5 * * * ? *)

CMyLambdaTarget

DLambdaTrigger

Attempts:

3 left

💡 Hint

Common Mistakes

Using cron expression incorrectly or confusing target Id with ARN.

The schedule expression 'rate(5 minutes)' triggers every 5 minutes. The target Id is a unique name like 'MyLambdaTarget'.

5fill in blank

hard

Fill all three blanks to create an S3 event notification that triggers Lambda on object deletion.

AWS

{
  "LambdaFunctionConfigurations": [
    {
      "LambdaFunctionArn": "arn:aws:lambda:us-east-1:123456789012:function:MyFunction",
      "Events": ["[1]"],
      "Filter": {
        "Key": {
          "FilterRules": [
            {"Name": "[2]", "Value": "[3]"}
          ]
        }
      }
    }
  ]
}

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

As3:ObjectRemoved:*

Bs3:ObjectCreated:*

Cprefix

Dsuffix

Attempts:

3 left

💡 Hint

Common Mistakes

Using 's3:ObjectCreated:*' instead of removal event.

The event 's3:ObjectRemoved:*' triggers on object deletion. The filter rule uses 'prefix' and 'suffix' to specify object key filtering.

Practice

1. Which AWS service event can automatically start a Lambda function when a new file is uploaded?

easy

A. AWS CloudTrail log event

B. Amazon EC2 instance launch event

C. Amazon S3 object upload event

D. Amazon RDS backup event

Solution

1. Step 1: Understand Lambda triggers

   Lambda functions can be triggered by events from various AWS services.

2. Step 2: Identify common event sources

   Amazon S3 triggers Lambda when a new object is uploaded to a bucket.

3. Final Answer:

   Amazon S3 object upload event -> Option C

4. Quick Check:

   S3 upload triggers Lambda = A [OK]

Hint: Remember: S3 uploads often trigger Lambda automatically [OK]

Common Mistakes:

• Confusing EC2 events as Lambda triggers
• Thinking CloudTrail logs directly trigger Lambda
• Assuming RDS backups trigger Lambda

2. Which of the following is the correct way to configure an SQS queue as an event source for a Lambda function?

easy

A. Enable CloudWatch Events on the SQS queue

B. Add an S3 trigger to the Lambda function

C. Attach an IAM role to the SQS queue

D. Create an event source mapping between the SQS queue and Lambda

Solution

1. Step 1: Know how Lambda connects to SQS

   Lambda uses event source mappings to poll messages from SQS queues.

2. Step 2: Identify correct configuration

   Creating an event source mapping links the SQS queue to Lambda for automatic invocation.

3. Final Answer:

   Create an event source mapping between the SQS queue and Lambda -> Option D

4. Quick Check:

   SQS triggers Lambda via event source mapping = D [OK]

Hint: Event source mapping links SQS to Lambda directly [OK]

Common Mistakes:

• Confusing S3 triggers with SQS triggers
• Attaching IAM roles to SQS instead of Lambda
• Using CloudWatch Events incorrectly for SQS

3. Given this Lambda trigger configuration snippet:

{
  "EventSourceArn": "arn:aws:sqs:us-east-1:123456789012:MyQueue",
  "FunctionName": "ProcessQueueMessages",
  "Enabled": true
}

What happens when a new message arrives in the SQS queue?

medium

A. The Lambda function ProcessQueueMessages is invoked automatically

B. The message is deleted from the queue without processing

C. The Lambda function is not triggered until manually invoked

D. An error occurs because the configuration is incomplete

Solution

1. Step 1: Understand event source mapping

   The snippet shows an event source mapping linking an SQS queue to a Lambda function.

2. Step 2: Effect of Enabled=true

   With Enabled set to true, Lambda polls the queue and invokes the function on new messages.

3. Final Answer:

   The Lambda function ProcessQueueMessages is invoked automatically -> Option A

4. Quick Check:

   Enabled event source mapping triggers Lambda = C [OK]

Hint: Enabled event source mapping means automatic Lambda invocation [OK]

Common Mistakes:

• Assuming manual invocation is needed
• Thinking messages get deleted without processing
• Believing configuration is incomplete without batch size

4. You configured a DynamoDB stream as a trigger for your Lambda function, but the function is not invoked when the table changes. What is the most likely cause?

medium

A. The DynamoDB stream is disabled or not enabled

B. The DynamoDB table has no data

C. The Lambda function code is empty

D. The Lambda execution role lacks permission to read the DynamoDB stream

Solution

1. Step 1: Check DynamoDB stream status

   For Lambda to trigger, the DynamoDB stream must be enabled on the table.

2. Step 2: Confirm stream is active

   If the stream is disabled or not enabled, no events are generated to invoke Lambda.

3. Final Answer:

   The DynamoDB stream is disabled or not enabled -> Option A

4. Quick Check:

   DynamoDB stream must be enabled for Lambda trigger = A [OK]

Hint: Ensure DynamoDB stream is enabled to trigger Lambda [OK]

Common Mistakes:

• Ignoring stream enablement status
• Assuming empty table stops triggers
• Blaming Lambda code without checking stream

5. You want a Lambda function to run every day at 6 AM UTC without any external event. Which AWS service and configuration should you use to trigger the Lambda?

hard

A. Configure an S3 bucket event to trigger Lambda at 6 AM

B. Create a CloudWatch Events (EventBridge) rule with a cron expression to trigger Lambda

C. Set up an SQS queue with a message sent daily at 6 AM

D. Enable DynamoDB Streams to trigger Lambda daily

Solution

1. Step 1: Identify scheduled triggers for Lambda

   To run Lambda on a schedule without external events, use CloudWatch Events (EventBridge) rules.

2. Step 2: Use cron expression in EventBridge

   Create a rule with a cron expression for 6 AM UTC daily to trigger the Lambda function automatically.

3. Final Answer:

   Create a CloudWatch Events (EventBridge) rule with a cron expression to trigger Lambda -> Option B

4. Quick Check:

   Scheduled Lambda uses EventBridge cron rule = B [OK]

Hint: Use EventBridge cron rules for scheduled Lambda runs [OK]

Common Mistakes:

• Trying to trigger Lambda via S3 or SQS for schedule
• Assuming DynamoDB Streams can schedule events
• Not using cron expressions for timing