Lambda function concept in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an AWS Lambda function?

An AWS Lambda function is a small piece of code that runs in the cloud without needing a server. It runs only when triggered and automatically scales.

beginner

How does AWS Lambda handle servers?

AWS Lambda automatically manages the servers for you. You don't have to set up or maintain any servers to run your code.

beginner

What triggers an AWS Lambda function to run?

A Lambda function runs when an event happens, like a file upload, a web request, or a timer. These events are called triggers.

intermediate

What is the maximum execution time for a Lambda function?

A Lambda function can run up to 15 minutes per invocation. After that, it stops automatically.

intermediate

How does AWS Lambda scale when many requests come in?

AWS Lambda automatically runs more copies of your function to handle many requests at the same time, scaling up and down as needed.

What do you need to manage when using AWS Lambda?

A Nothing, AWS manages the servers

B You must set up virtual machines

C You need to install operating systems

D You must configure physical hardware

AWS Lambda is serverless, so AWS manages all server infrastructure.

Which of these can trigger a Lambda function?

A A local computer shutdown

B A manual server reboot

C A file uploaded to cloud storage

D A printer error

Events like file uploads in cloud storage can trigger Lambda functions.

What is the maximum time a Lambda function can run per invocation?

A 5 minutes

B Unlimited

C 1 hour

D 15 minutes

Lambda functions have a maximum execution time of 15 minutes.

How does Lambda handle many requests at once?

A It queues requests and processes one at a time

B It automatically runs multiple copies of the function

C It rejects extra requests

D It requires manual scaling

Lambda automatically scales by running multiple instances of your function.

Which of these is NOT a benefit of AWS Lambda?

A Requires manual patching of servers

B No server management

C Pay only for compute time used

D Automatic scaling

Lambda does not require manual patching; AWS handles that.

Explain in simple terms what an AWS Lambda function is and how it works.

Think about how a light turns on only when you flip a switch.

Describe the main advantages of using AWS Lambda compared to traditional servers.

Imagine not having to worry about the kitchen when cooking a meal.

Practice

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

easy

A. To store large amounts of data

B. To run code automatically without managing servers

C. To create virtual machines

D. To manage user permissions

Solution

1. Step 1: Understand Lambda's role

   AWS Lambda runs your code without needing you to manage servers.

2. Step 2: Compare options

   Options A, C, and D describe other AWS services, not Lambda.

3. Final Answer:

   To run code automatically without managing servers -> Option B

4. Quick Check:

   Lambda = serverless code execution [OK]

Hint: Lambda runs code without servers, not storage or VMs [OK]

Common Mistakes:

• Confusing Lambda with storage services
• Thinking Lambda creates virtual machines
• Assuming Lambda manages user permissions

2. Which of the following is the correct way to define a simple AWS Lambda function handler in Python?

easy

A. lambda handler(event): print('Hello World')

B. function handler(event) { return 'Hello World'; }

C. def handler(event, context): return 'Hello World'

D. def handler(): print('Hello World')

Solution

1. Step 1: Identify correct Python Lambda handler syntax

   Lambda handlers in Python must accept two parameters: event and context.

2. Step 2: Check each option

   def handler(event, context): return 'Hello World' correctly defines a Python function with event and context parameters and returns a string. function handler(event) { return 'Hello World'; } is JavaScript syntax. lambda handler(event): print('Hello World') misuses lambda keyword. def handler(): print('Hello World') lacks required parameters.

3. Final Answer:

   def handler(event, context): return 'Hello World' -> Option C

4. Quick Check:

   Python Lambda handler needs event and context [OK]

Hint: Python Lambda handlers always have (event, context) parameters [OK]

Common Mistakes:

• Using JavaScript syntax in Python Lambda
• Omitting event or context parameters
• Misusing lambda keyword for handler

3. Given this AWS Lambda Python code:

def handler(event, context):
    name = event.get('name', 'Guest')
    return f"Hello, {name}!"

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

medium

A. "Hello, Guest!"

B. "Hello, None!"

C. Error: 'name' key missing

D. "Hello, !"

Solution

1. Step 1: Analyze event input and code behavior

   The event is an empty dictionary, so event.get('name', 'Guest') returns the default 'Guest'.

2. Step 2: Determine return value

   The function returns the string "Hello, Guest!" because 'name' is not in event.

3. Final Answer:

   "Hello, Guest!" -> Option A

4. Quick Check:

   Missing key uses default value 'Guest' [OK]

Hint: event.get with default returns default if key missing [OK]

Common Mistakes:

• Assuming missing key causes error
• Thinking None is returned instead of default
• Ignoring default value in get()

4. You wrote this AWS Lambda function in Python:

def handler(event, context):
    return event['message']

When triggered with event {}, it throws a KeyError. How can you fix it?

medium

A. Use event.get('message', 'No message') instead of event['message']

B. Remove the return statement

C. Add a print statement before return

D. Change function name to lambda_handler

Solution

1. Step 1: Identify cause of KeyError

   Accessing event['message'] when 'message' key is missing causes KeyError.

2. Step 2: Use safe access method

   Replacing event['message'] with event.get('message', 'No message') avoids error by providing default.

3. Final Answer:

   Use event.get('message', 'No message') instead of event['message'] -> Option A

4. Quick Check:

   Use get() to avoid KeyError on missing keys [OK]

Hint: Use get() with default to prevent KeyError [OK]

Common Mistakes:

• Ignoring missing key causes error
• Thinking print fixes KeyError
• Assuming function name affects key access

5. You want an AWS Lambda function to process image uploads to S3 and resize them. Which combination of AWS services and Lambda features is best suited for this task?

hard

A. Use Lambda to create EC2 instances that resize images

B. Run Lambda on a schedule to scan S3 and resize images manually

C. Upload images directly to Lambda storage for resizing

D. Use S3 event trigger on object creation to invoke Lambda, which resizes images and saves back to S3

Solution

1. Step 1: Understand event-driven processing

   S3 can trigger Lambda automatically when new objects are created, ideal for immediate processing.

2. Step 2: Evaluate options for image resizing

   Use S3 event trigger on object creation to invoke Lambda, which resizes images and saves back to S3 uses S3 event triggers and Lambda to resize and save images back to S3, which is efficient and serverless. Run Lambda on a schedule to scan S3 and resize images manually delays processing and requires scanning. Use Lambda to create EC2 instances that resize images misuses Lambda to create servers. Upload images directly to Lambda storage for resizing is invalid as Lambda has no persistent storage for uploads.

3. Final Answer:

   Use S3 event trigger on object creation to invoke Lambda, which resizes images and saves back to S3 -> Option D

4. Quick Check:

   S3 event triggers + Lambda = best for image processing [OK]

Hint: Use S3 event triggers to run Lambda on uploads [OK]

Common Mistakes:

• Thinking Lambda can store files persistently
• Using scheduled scans instead of event triggers
• Misusing Lambda to create servers