How to respond to viewers without sending the request to the origin?

Question

I am trying to implement in python a lambda edge that receives a file, evaluates it with the length of the content and if it is greater than allowed, respond to the viewer something without sending the request to the origin, otherwise it will be sent to S3. I have already implemented the part to sent to S3, but im struggling with responding to the viewer.

Answer 1

You can generate a custom response to the request events triggers

Sample:

import json

def lambda_handler(event, context):
    if True: # Case where you want to return the response
        response = {
            'body': "SAMPLE RESPONSE", # For image set this to base64 encoded string
            'bodyEncoding': 'text',
            'status': '200',
            'statusDescription': 'OK',
            'headers': {
            'content-type':
                [
                    {
                    'key': 'Content-Type',
                    'value': 'text'
                    }
                ]
            }
        }

        return response
    else: # Case where you want the request to be forwarded to the origin server
        return event['Records'][0]['cf']['request']

Note: There will be some limitations on response size in case of returning response for request events. They can be found on Amazon developer guide