AWS Lambda Function Tutorial

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1. Basic Lambda Function

Example 1: Hello World Lambda

import json

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

Explanation

1. Imports the JSON module to format responses.

   • import json

2. Defines the Lambda function entry point.

   • def lambda_handler(event, context):

3. Returns an HTTP response with a 200 status.

   • return {'statusCode': 200, 'body': json.dumps('Hello from AWS Lambda!')}

4. AWS automatically executes this function when triggered.

   • lambda_handler(event, context)

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Example 2: Returning Event Data

def lambda_handler(event, context):
    return {
        'statusCode': 200,
        'body': json.dumps(event)
    }

Explanation

1. Receives an event from AWS services.

   • def lambda_handler(event, context):

2. Sends the event data back in the response.

   • 'body': json.dumps(event)

3. Ensures the response is JSON formatted.

   • json.dumps(event)

4. Useful for debugging event structures.

   • return {...}

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Example 3: Returning Custom Headers

def lambda_handler(event, context):
    return {
        'statusCode': 200,
        'headers': {'Content-Type': 'application/json'},
        'body': json.dumps({'message': 'Custom headers added'})
    }

Explanation

1. Adds a custom response header.

   • 'headers': {'Content-Type': 'application/json'}

2. Returns a JSON response with custom data.

   • 'body': json.dumps({'message': 'Custom headers added'})

3. Ensures proper HTTP status codes.

   • 'statusCode': 200

4. Useful when integrating with REST APIs.

   • lambda_handler(event, context)

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Example 4: Using Query Parameters

def lambda_handler(event, context):
    name = event.get('queryStringParameters', {}).get('name', 'Guest')
    return {
        'statusCode': 200,
        'body': json.dumps(f'Hello, {name}!')
    }

Explanation

1. Extracts query parameters from the event.

   • name = event.get('queryStringParameters', {}).get('name', 'Guest')

2. Defaults to ‘Guest’ if no parameter is provided.

   • .get('name', 'Guest')

3. Returns a dynamic greeting message.

   • 'body': json.dumps(f'Hello, {name}!')

4. Useful for API Gateway requests.

   • lambda_handler(event, context)

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2. AWS Lambda with DynamoDB

Example 1: Insert Data into DynamoDB

import boto3

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('Users')

def lambda_handler(event, context):
    table.put_item(Item={'UserID': event['UserID'], 'Name': event['Name']})
    return {'statusCode': 200, 'body': 'User added'}

Explanation

1. Connects AWS Lambda to DynamoDB.

   • dynamodb = boto3.resource('dynamodb')

2. Gets reference to the Users table.

   • table = dynamodb.Table('Users')

3. Inserts user data into the table.

   • table.put_item(Item={'UserID': event['UserID'], 'Name': event['Name']})

4. Confirms successful insertion.

   • return {'statusCode': 200, 'body': 'User added'}

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Example 2: Fetch Data from DynamoDB

def lambda_handler(event, context):
    response = table.get_item(Key={'UserID': event['UserID']})
    return {'statusCode': 200, 'body': json.dumps(response.get('Item', 'User not found'))}

Explanation

1. Fetches an item from DynamoDB using UserID.

   • response = table.get_item(Key={'UserID': event['UserID']})

2. Returns the retrieved item if it exists.

   • json.dumps(response.get('Item', 'User not found'))

3. Handles missing users gracefully.

   • response.get('Item', 'User not found')

4. Useful for API-based retrieval operations.

   • return {'statusCode': 200, 'body': ...}

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Example 3: Update an Item in DynamoDB

def lambda_handler(event, context):
    table.update_item(
        Key={'UserID': event['UserID']},
        UpdateExpression="set Name=:n",
        ExpressionAttributeValues={':n': event['Name']}
    )
    return {'statusCode': 200, 'body': 'User updated'}

Explanation

1. Updates user data using an expression.

   • UpdateExpression="set Name=:n"

2. Uses ExpressionAttributeValues to avoid injection.

   • ExpressionAttributeValues={':n': event['Name']}

3. Ensures atomic updates without overwriting all fields.

   • table.update_item(...)

4. Confirms the update in response.

   • return {'statusCode': 200, 'body': 'User updated'}

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Example 4: Delete a User from DynamoDB

def lambda_handler(event, context):
    table.delete_item(Key={'UserID': event['UserID']})
    return {'statusCode': 200, 'body': 'User deleted'}

Explanation

1. Deletes a user record from DynamoDB.

   • table.delete_item(Key={'UserID': event['UserID']})

2. Ensures efficient deletion using the primary key.

   • delete_item(Key={'UserID': event['UserID']})

3. Reduces storage usage by removing old records.

   • return {'statusCode': 200, 'body': 'User deleted'}

4. Useful for user account removals.

   • lambda_handler(event, context)

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3. AWS Lambda with S3

Example 1: Upload File to S3

import boto3

s3 = boto3.client('s3')

def lambda_handler(event, context):
    s3.upload_file('/tmp/sample.txt', 'my-bucket', 'sample.txt')
    return {'statusCode': 200, 'body': 'File uploaded'}

Explanation

1. Creates an S3 client for interacting with AWS S3.

   • s3 = boto3.client('s3')

2. Uploads a file from Lambda to S3.

   • s3.upload_file('/tmp/sample.txt', 'my-bucket', 'sample.txt')

3. Uses ‘/tmp/’ for temporary Lambda storage.

   • '/tmp/sample.txt'

4. Returns a success message after upload.

   • return {'statusCode': 200, 'body': 'File uploaded'}

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Example 2: Read File from S3

def lambda_handler(event, context):
    obj = s3.get_object(Bucket='my-bucket', Key='sample.txt')
    return {'statusCode': 200, 'body': obj['Body'].read().decode('utf-8')}

Explanation

1. Fetches a file from S3 storage.

   • s3.get_object(Bucket='my-bucket', Key='sample.txt')

2. Reads the file content into memory.

   • obj['Body'].read().decode('utf-8')

3. Decodes UTF-8 to make it human-readable.

   • .decode('utf-8')

4. Returns the file content as a response.

   • return {'statusCode': 200, 'body': ...}

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