Creating a Lambda function in AWS - Practice Exercises

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when a Lambda function is invoked with an event?

Consider an AWS Lambda function configured with a handler that processes incoming events. What is the expected behavior when the function is invoked with a valid event?

A The Lambda function deletes the event without processing it.

B The Lambda function stores the event in S3 and does not execute any code.

C The Lambda function automatically scales to multiple instances without running the handler.

D The Lambda function executes the handler code with the event data and returns a response or error.

💡 Hint

Think about what a Lambda function is designed to do when triggered.

When a Lambda function is invoked, it runs the handler code with the event data and returns a result or error. It does not store or delete events automatically.

❓ Configuration

intermediate

Which IAM role policy allows a Lambda function to write logs to CloudWatch?

You want your Lambda function to write logs to CloudWatch Logs. Which IAM policy statement should be attached to the Lambda execution role?

A {"Effect": "Deny", "Action": ["logs:CreateLogGroup"], "Resource": "*"}

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

C {"Effect": "Allow", "Action": ["ec2:StartInstances"], "Resource": "*"}

D {"Effect": "Allow", "Action": ["s3:PutObject"], "Resource": "arn:aws:s3:::my-bucket/*"}

💡 Hint

Focus on permissions related to CloudWatch Logs actions.

To allow Lambda to write logs, the role needs permissions to create log groups, streams, and put log events in CloudWatch Logs.

❓ Architecture

advanced

How to design a Lambda function for high availability and fault tolerance?

You need to design a Lambda function that remains highly available and fault tolerant in case of failures. Which architecture approach best achieves this?

A Disable CloudWatch Logs to improve performance and reduce failure points.

B Deploy the Lambda function only in one Availability Zone to reduce latency.

C Deploy the Lambda function in multiple AWS Regions and use Route 53 latency-based routing to invoke the nearest function.

D Use a single Lambda function with no retries configured to avoid duplicate processing.

💡 Hint

Consider geographic redundancy and routing to improve availability.

Deploying Lambda functions in multiple regions with latency-based routing ensures availability even if one region fails.

❓ security

advanced

What is the best practice to secure environment variables in Lambda functions?

You want to store sensitive data like API keys in Lambda environment variables securely. What is the best practice to protect these secrets?

A Encrypt environment variables using AWS KMS and enable Lambda to decrypt them at runtime.

B Store secrets directly in plain text environment variables without encryption.

C Hardcode secrets inside the Lambda function code for faster access.

D Send secrets as part of the event payload when invoking the Lambda function.

💡 Hint

Think about encryption and secure key management.

Encrypting environment variables with AWS KMS and allowing Lambda to decrypt them at runtime protects secrets from exposure.

✅ Best Practice

expert

How to optimize cold start performance for a Lambda function written in Java?

Java Lambda functions often have longer cold start times. Which approach best reduces cold start latency?

A Use provisioned concurrency to keep Lambda instances initialized and ready to serve requests.

B Increase the memory allocation to the minimum value to reduce startup time.

C Avoid using any dependencies and write all code inline in the handler method.

D Disable VPC access to reduce network initialization delays.

💡 Hint

Consider AWS features that keep functions warm.

Provisioned concurrency keeps Lambda instances initialized, reducing cold start latency especially for Java functions.

Practice

1. What is the main purpose of an AWS Lambda function?

easy

A. To run code without managing servers

B. To store large amounts of data

C. To create virtual machines

D. To manage user permissions

Solution

1. Step 1: Understand Lambda's role

   AWS Lambda lets you run code without needing to manage servers or infrastructure.

2. Step 2: Compare options

   The incorrect options describe other AWS services such as user permissions (IAM), data storage (S3), and virtual machines (EC2).

3. Final Answer:

   To run code without managing servers -> Option A

4. Quick Check:

   Lambda = serverless code execution [OK]

Hint: Lambda runs code without servers [OK]

Common Mistakes:

• Confusing Lambda with storage services
• Thinking Lambda manages servers
• Mixing Lambda with user management

2. Which of the following is the correct way to specify the handler when creating a Lambda function in AWS?

easy

A. handler.index

B. index.handler

C. lambda.handler

D. handler.lambda

Solution

1. Step 1: Understand handler format

   The handler is specified as filename.functionname. Commonly, the file is index and function is handler.

2. Step 2: Match options

   Only index.handler matches the correct format; others reverse or misuse parts.

3. Final Answer:

   index.handler -> Option B

4. Quick Check:

   Handler = filename.function [OK]

Hint: Handler format is filename.functionname [OK]

Common Mistakes:

• Swapping filename and function name
• Using invalid handler names
• Confusing handler with runtime

3. Given this AWS Lambda function code snippet in Python:

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

What will be the output if the event is {}?

medium

A. "default"

B. None

C. Error

D. "key"

Solution

1. Step 1: Analyze the handler function

   The function returns the value of 'key' from event, or 'default' if 'key' is missing.

2. Step 2: Check the event input

   The event is an empty dictionary, so 'key' is not present, so it returns 'default'.

3. Final Answer:

   "default" -> Option A

4. Quick Check:

   Missing key returns default [OK]

Hint: Missing dict key returns default value [OK]

Common Mistakes:

• Assuming missing key returns None
• Expecting an error on missing key
• Confusing key name with value

4. You created a Lambda function but it fails with a permissions error when invoked. What is the most likely cause?

medium

A. The deployment package is too large

B. The handler name is incorrect

C. The runtime is not supported

D. The Lambda execution role lacks necessary permissions

Solution

1. Step 1: Understand permissions in Lambda

   Lambda functions need an IAM role with permissions to run and access resources.

2. Step 2: Identify cause of permissions error

   A permissions error usually means the execution role is missing required permissions.

3. Final Answer:

   The Lambda execution role lacks necessary permissions -> Option D

4. Quick Check:

   Permissions error = missing IAM role rights [OK]

Hint: Check IAM role permissions for Lambda [OK]

Common Mistakes:

• Blaming handler name for permissions error
• Ignoring IAM role setup
• Assuming runtime causes permissions error

5. You want to create a Lambda function that processes images uploaded to an S3 bucket. Which combination of settings is required to ensure the Lambda runs automatically when a new image is uploaded?

hard

A. Set Lambda runtime to Node.js and upload images directly to Lambda

B. Manually invoke Lambda after uploading images to S3

C. Set S3 event trigger on bucket for 'ObjectCreated' and assign Lambda execution role with S3 read permissions

D. Create an EC2 instance to monitor S3 and call Lambda

Solution

1. Step 1: Configure S3 event trigger

   To run Lambda automatically on uploads, configure S3 to trigger Lambda on 'ObjectCreated' events.

2. Step 2: Assign correct IAM role permissions

   Lambda needs an execution role with permissions to read from S3 to process images.

3. Final Answer:

   Set S3 event trigger on bucket for 'ObjectCreated' and assign Lambda execution role with S3 read permissions -> Option C

4. Quick Check:

   S3 trigger + IAM role = automatic Lambda run [OK]

Hint: Use S3 event triggers with proper IAM role [OK]

Common Mistakes:

• Thinking manual invocation is automatic
• Confusing runtime with event triggers
• Using EC2 unnecessarily for Lambda triggers