Lambda handler function structure in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the correct AWS Lambda handler signature

Which of the following AWS Lambda handler function signatures is correct for Node.js?

A function handler(event) { return 'done'; }

B exports.handler = (context, event) => { return 'done'; }

C exports.handler = async (event, context) => { return 'done'; }

D handler = (event, context, callback) => { return 'done'; }

💡 Hint

Remember the order of parameters: event first, then context.

The correct AWS Lambda handler in Node.js receives event as the first parameter and context as the second. It can be async and return a value or use a callback.

❓ Configuration

intermediate

Determine the output of a Python Lambda handler

What is the output when this AWS Lambda Python handler is invoked with {"key": "value"} as event?

AWS

def lambda_handler(event, context):
    return event.get('key', 'default')

A "value"

B "default"

C None

D KeyError

💡 Hint

Check how dict.get() works in Python.

The get method returns the value for the key if it exists; otherwise, it returns the default. Here, 'key' exists with value 'value'.

❓ Architecture

advanced

Choose the best event source for a Lambda function triggered by file uploads

You want to run a Lambda function automatically whenever a new file is uploaded to an S3 bucket. Which event source configuration is correct?

A Set up CloudWatch Events to poll the S3 bucket every minute

B Configure S3 bucket event notifications to trigger Lambda on 's3:ObjectCreated:*' events

C Use API Gateway to invoke Lambda when files are uploaded

D Manually invoke Lambda from an EC2 instance after upload

💡 Hint

Think about native S3 event triggers for Lambda.

S3 can directly trigger Lambda functions on object creation events, making option B the best and most efficient choice.

❓ security

advanced

Identify the least privilege IAM policy for Lambda execution

Which IAM policy grants the least privilege necessary for a Lambda function to write logs to CloudWatch?

A { "Effect": "Allow", "Action": ["logs:CreateLogGroup", "logs:CreateLogStream", "logs:PutLogEvents"], "Resource": "arn:aws:logs:*:*:*" }

B { "Effect": "Allow", "Action": "*", "Resource": "*" }

C { "Effect": "Allow", "Action": ["logs:PutLogEvents"], "Resource": "*" }

D { "Effect": "Allow", "Action": ["logs:CreateLogGroup", "logs:CreateLogStream"], "Resource": "arn:aws:logs:*:*:*" }

💡 Hint

Consider all actions needed to create and write logs.

Option A includes all necessary actions with resource restriction, following least privilege. Option A is too broad. Option A misses creating groups and streams. Option A misses putting log events.

❓ service_behavior

expert

Predict Lambda function behavior with asynchronous invocation and error handling

A Lambda function is invoked asynchronously. It throws an exception during execution. What happens to the event and error?

A The event is lost immediately with no retries or notifications

B The error is returned immediately to the caller

C The function retries indefinitely until it succeeds

D The event is retried twice by default, then sent to a dead-letter queue if configured

💡 Hint

Think about Lambda's default retry behavior for asynchronous calls.

For asynchronous invocations, Lambda retries failed executions twice by default. If a dead-letter queue is set, the event is sent there after retries fail.