Creating a Lambda function in AWS - Visual Walkthrough

Process Flow - Creating a Lambda function

Write Lambda code

↓

Package code and dependencies

↓

Create Lambda function in AWS

↓

Upload code package

↓

Set function configuration

↓

Test Lambda function

↓

Function ready to invoke

This flow shows the steps to create and deploy a Lambda function: write code, package it, create the function in AWS, upload code, configure, test, and then use it.

Execution Sample

AWS

def lambda_handler(event, context):
    return {'statusCode': 200, 'body': 'Hello from Lambda!'}

A simple Lambda function that returns a success status and a greeting message.

Process Table

Step	Action	Details	Result
1	Write Lambda code	Define lambda_handler function	Code ready
2	Package code	Create deployment package zip	Package created
3	Create Lambda function	Use AWS console or CLI	Function created with name 'MyLambda'
4	Upload code	Upload zip package to Lambda	Code uploaded
5	Set configuration	Set runtime to Python 3.12, handler to lambda_handler.lambda_handler	Configuration set
6	Test function	Invoke test event	Returns statusCode 200 and body 'Hello from Lambda!'
7	Function ready	Ready for real invocations	Lambda function deployed successfully

💡 All steps completed successfully; Lambda function is deployed and ready.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	After Step 6	Final
lambda_handler	undefined	function defined	packaged in zip	uploaded to AWS	tested with event	ready for invocation
deployment_package	none	none	zip file created	uploaded	unchanged	unchanged
lambda_function_status	not created	not created	created	code uploaded	tested	deployed

Key Moments - 3 Insights

Why do we need to package the code before uploading?

Packaging bundles your code and dependencies into one file, which AWS Lambda requires to deploy the function, as shown in step 2 and 4 of the execution_table.

What does the handler setting mean in the configuration?

The handler tells Lambda which function to run when invoked. In step 5, setting it to 'lambda_handler.lambda_handler' connects AWS to your code's entry point.

Why test the function after uploading?

Testing (step 6) confirms the function runs correctly in AWS environment before real use, ensuring no errors in deployment or code.

Visual Quiz - 3 Questions

Look at the execution_table, what is the result after step 3?

A Code uploaded

B Package created

C Function created with name 'MyLambda'

D Function tested

💡 Hint

Check the 'Result' column for step 3 in the execution_table.

At which step is the Lambda function tested?

A Step 6

B Step 5

C Step 4

D Step 7

💡 Hint

Look for the step with action 'Test function' in the execution_table.

If the packaging step is skipped, what will likely happen?

A Function will be created successfully

B Code upload will fail or be incomplete

C Function will test successfully

D Configuration will be set automatically

💡 Hint

Refer to step 2 and 4 in the execution_table about packaging and uploading.

Concept Snapshot

Creating a Lambda function:
1. Write your function code with a handler.
2. Package code and dependencies into a zip file.
3. Create the Lambda function in AWS.
4. Upload the package and set runtime and handler.
5. Test the function to verify it works.
6. Function is ready to be invoked.

Full Transcript

To create a Lambda function, first write your function code with a handler named lambda_handler. Then package this code and any dependencies into a zip file. Next, create the Lambda function in AWS using the console or CLI. Upload your zip package to the function and set the runtime environment and handler name. After uploading, test the function with a sample event to ensure it runs correctly. Once tested successfully, the Lambda function is ready for real use.

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