Creating a Lambda function in AWS - Quick Revision & Summary

Recall & Review

beginner

What is AWS Lambda?

AWS Lambda is a service that lets you run code without managing servers. You just upload your code, and Lambda runs it when needed.

beginner

What is a trigger in AWS Lambda?

A trigger is an event that starts your Lambda function, like a file upload or a web request.

intermediate

Why do you need an execution role for a Lambda function?

The execution role gives your Lambda permission to access other AWS services it needs, like reading from a database.

intermediate

What is the maximum duration a Lambda function can run?

A Lambda function can run up to 15 minutes before it times out.

beginner

How do you update the code of an existing Lambda function?

You can update the code by uploading a new file or using the AWS Console editor, AWS CLI, or SDKs.

What do you need to provide when creating a Lambda function?

A A virtual machine image

B Code and an execution role

C A database connection string

D A server to run the code

You must provide your code and an execution role that grants permissions for the Lambda function.

Which AWS service can trigger a Lambda function?

A Amazon EC2

B AWS IAM

C AWS CloudFormation

D Amazon S3

Amazon S3 can trigger Lambda functions on events like file uploads.

What is the maximum timeout for a Lambda function?

A 5 minutes

B 30 minutes

C 15 minutes

D 60 minutes

Lambda functions can run up to 15 minutes before timing out.

How do you give a Lambda function permission to access other AWS services?

A By assigning an execution role

B By adding a trigger

C By uploading code

D By setting environment variables

An execution role grants the Lambda function permissions to access AWS resources.

Which language can you NOT use to write Lambda functions?

A COBOL

B JavaScript

C Ruby

D Python

COBOL is not supported by AWS Lambda.

Explain the steps to create a Lambda function from scratch.

Think about what you need before the function can run and respond to events.

Describe how Lambda functions handle scaling when many events happen at once.

Imagine many friends calling you at the same time and you can talk to all of them separately.

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