Lambda with S3 event triggers in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when an S3 event triggers a Lambda function?

An S3 bucket is configured to trigger a Lambda function on object creation. What is the expected behavior when a new file is uploaded?

A The S3 bucket sends an email notification instead of triggering Lambda.

B The Lambda function runs only if the file is larger than 1 GB.

C The Lambda function must be manually invoked after the file upload.

D The Lambda function runs automatically with event details about the new file.

💡 Hint

Think about how event-driven services work in AWS.

When an S3 event trigger is set, Lambda automatically runs with details of the event, such as the file uploaded.

❓ Configuration

intermediate

Which IAM permission is required for Lambda to read an S3 object?

You want your Lambda function to read files from an S3 bucket when triggered. Which IAM permission must be included in the Lambda execution role?

A "s3:GetObject" permission on the bucket

B "s3:PutObject" permission on the bucket

C "s3:DeleteObject" permission on the bucket

D "lambda:InvokeFunction" permission on the bucket

💡 Hint

Consider what action Lambda needs to do to read a file.

To read files from S3, Lambda needs the "s3:GetObject" permission on the bucket or objects.

❓ Architecture

advanced

How to design a fault-tolerant Lambda triggered by S3 events?

You want to ensure your Lambda function processes every S3 upload event even if it fails initially. Which architecture best supports this?

A Use S3 event to trigger Lambda without retries or error handling.

B Set Lambda timeout to 1 second and ignore failures.

C Configure S3 event to trigger Lambda with a dead-letter queue (DLQ) for failed events.

D Manually re-upload files if Lambda fails to process them.

💡 Hint

Think about how to handle failures automatically.

Using a DLQ allows failed Lambda invocations to be captured and retried or inspected later, improving fault tolerance.

❓ security

advanced

What is the safest way to restrict Lambda access to only one S3 bucket?

You want your Lambda function to access only a specific S3 bucket and no others. Which IAM policy condition achieves this?

A Use a policy with "Resource" set to the specific bucket ARN and "Action" to "s3:GetObject".

B Grant "s3:*" permission on all buckets and rely on Lambda code to check bucket name.

C Attach a policy allowing "s3:GetObject" on "arn:aws:s3:::*" (all buckets).

D Use a policy with "Condition" to allow access only during business hours.

💡 Hint

Restrict permissions by resource ARN rather than broad access.

Limiting the IAM policy "Resource" to the specific bucket ARN restricts Lambda access to only that bucket.

✅ Best Practice

expert

How to optimize Lambda cold start time when triggered by S3 events?

Your Lambda function triggered by S3 events has high cold start latency. Which approach best reduces this delay?

A Increase Lambda memory to maximum without testing impact.

B Use provisioned concurrency to keep Lambda instances warm.

C Disable S3 event triggers and invoke Lambda manually.

D Use a larger S3 bucket to speed up event delivery.

💡 Hint

Think about how to keep Lambda ready to run instantly.

Provisioned concurrency keeps Lambda instances initialized and ready, reducing cold start latency significantly.