Event triggers for Lambda in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

How does an S3 event trigger a Lambda function?

When a new file is uploaded to an S3 bucket, which event trigger configuration will cause a Lambda function to run automatically?

A Configure the Lambda function with an S3 trigger for the 's3:ObjectCreated:*' event on the bucket.

B Set up a CloudWatch alarm on the bucket and link it to the Lambda function.

C Create an SNS topic subscribed by the Lambda function and publish messages manually.

D Enable versioning on the bucket and link it to the Lambda function.

💡 Hint

Think about which S3 event directly relates to new file uploads and can invoke Lambda automatically.

The 's3:ObjectCreated:*' event triggers Lambda when a new object is created in the bucket. CloudWatch alarms and SNS require manual or indirect setup. Versioning alone does not trigger Lambda.

❓ Architecture

intermediate

Which AWS service can trigger Lambda on a scheduled basis?

You want a Lambda function to run every day at midnight automatically. Which AWS service should you use to trigger it?

A AWS Config

B AWS CloudTrail

C Amazon SNS topic with daily messages

D Amazon EventBridge (CloudWatch Events) with a scheduled rule

💡 Hint

Consider which service is designed to run tasks on a schedule.

Amazon EventBridge (formerly CloudWatch Events) supports scheduled rules to trigger Lambda functions at fixed times. CloudTrail and Config track changes but don't schedule tasks. SNS requires manual message publishing.

❓ security

advanced

What IAM permission is required for S3 to invoke a Lambda function?

To allow an S3 bucket to trigger a Lambda function on object creation, which IAM permission must be granted?

A s3:PutObject permission granted to the Lambda execution role

B lambda:InvokeFunction permission granted to the S3 service principal

C lambda:CreateFunction permission granted to the S3 bucket

D iam:PassRole permission granted to the Lambda function

💡 Hint

Think about what permission allows one service to call another.

S3 needs permission to invoke the Lambda function, which is granted by allowing the 'lambda:InvokeFunction' action to the S3 service principal. The other permissions are unrelated or incorrect for this trigger.

✅ Best Practice

advanced

How to avoid duplicate Lambda executions from SQS triggers?

You configured an SQS queue to trigger a Lambda function. Sometimes the function processes the same message twice. What is the best way to reduce duplicates?

A Delete messages from the queue immediately after Lambda invocation starts.

B Increase the Lambda timeout to avoid retries.

C Enable Lambda's event source mapping with batch size 1 and use idempotent processing in the function.

D Disable the SQS queue's dead-letter queue.

💡 Hint

Consider how Lambda processes messages and what can cause duplicates.

Setting batch size to 1 and making the function idempotent helps handle retries and avoid duplicate effects. Deleting messages too early or disabling dead-letter queues can cause message loss or unhandled failures.

🧠 Conceptual

expert

What happens if a Lambda function triggered by DynamoDB Streams fails repeatedly?

A Lambda function is triggered by DynamoDB Streams on table updates. If the function keeps failing for the same batch of records, what is the expected behavior?

A Lambda retries processing the batch until successful or the data expires in the stream (24 hours).

B Lambda skips the failed batch and moves to the next batch immediately.

C DynamoDB deletes the failed records from the stream after 5 retries.

D The Lambda function is disabled automatically after 3 failures.

💡 Hint

Think about how Lambda handles stream event retries and retention.

Lambda retries the same batch until it succeeds or the records expire from the DynamoDB stream (usually 24 hours). It does not skip or delete records automatically, nor disables itself.