lambda-breakdown.md

Lambda Function Breakdown

Imports and Logger Setup

import json
import logging

logger = logging.getLogger()
logger.setLevel(logging.INFO)

• Prepares logging and JSON handling.
• logger is used to record events and errors for debugging or monitoring.

Main Entry Point

def lambda_handler(event, context):

This is the function AWS Lambda calls when triggered.

• event: contains request data (e.g., HTTP body, headers).
• context: contains runtime info (e.g., function name, memory limit)

Log the Incoming Event

logger.info(f'Event received: {event}')

Logs the full incoming request for visibility.

Parse the Request Body

if isinstance(event.get('body'), str):
    body = json.loads(event['body'])
else:
    body = event.get('body', {})

Checks if the body is a string (typical in API Gateway):

• If so, parses it as JSON.
• If not, assumes it's already a dictionary.

Handle Invalid JSON

except json.JSONDecodeError:
    return {
        'statusCode': 400,
        ...
        'body': json.dumps({'error': 'Invalid JSON in request body'})
    }

If parsing fails, returns a 400 Bad Request with an error message.

Extract and Validate name

name = body.get('name', '').strip()

if not name:
    return {
        'statusCode': 400,
        ...
        'body': json.dumps({'error': 'Name is required'})
    }

• Tries to get the name field from the body.
• Strips whitespace and checks if it’s empty.
• If missing or blank, returns a 400 error.

Return a Greeting

response = {
    'statusCode': 200,
    ...
    'body': json.dumps({
        'message': f'Hello {name}!'
    })
}

If everything is valid, returns a 200 (OK) with a personalized greeting.

Send the Response

return response
Final step: sends the response back to the caller (e.g., API Gateway).

Example Input / Output

INPUT:

{
  "body": "{\"name\": \"Frankie\"}"
}

OUTPUT:

{
  "statusCode": 200,
  "body": "{\"message\": \"Hello Frankie!\"}"
}