lambda_function.py

import boto3
import io
from botocore.vendored import requests
s3 = boto3.resource('s3')


def lambda_handler(event, context):
    for record in event['Records']:
        buf = io.BytesIO()
        s3.Object(
            record['s3']['bucket']['name'],
            record['s3']['object']['key']
        ).download_fileobj(buf)
        resp = requests.post("WEBHOOK URL GOES HERE", files={'file': buf.getvalue()})
        # DO SOMETHING WITH THE RESPONSE

template.yaml

AWSTemplateFormatVersion: 2010-09-09
Transform: AWS::Serverless-2016-10-31
Description: A Lambda function to look for missing children in uploads to an S3 bucket

Parameters:
  Bucket:
    Type: String
    Description: "The S3 Bucket you want to enable the lambda for"

Resources:
  HitWebHookFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: lambda_function.lambda_handler
      Policies: AmazonS3ReadOnlyAccess
      Runtime: python36
      CodeURI: s3://<where_you_keep_your_code>/s3_processor.zip
      Events:
        PhotoUpload:
          Type: S3
          Properties:
            Bucket: !Sub "arn:aws:s3:::${Bucket}"
            Events: s3:ObjectCreated:*