aws-secrets-manager-rotation-lambdas VS cloudformation-templates

Create a new Lambda function that will handle the rotation - here is a template https://github.com/aws-samples/aws-secrets-manager-rotation-lambdas/blob/master/SecretsManagerRDSMySQLRotationMultiUser/lambda_function.py - I created it in a separate folder within the same repository. If you are like me, new to using Python, you could use this helpful guide:https://docs.aws.amazon.com/lambda/latest/dg/python-package.html.

One extra benefit of using Secrets Manager is that you can enable secret rotation. You can find reference implementations for the rotation lambda here https://github.com/aws-samples/aws-secrets-manager-rotation-lambdas

I would like to deploy SecretsManagerRDSPostgreSQLRotationMultiUser lambda with terraform; meaning I would store source code of lambda linked above in my repository and use terraform to package it into zip file, including dependencies and then upload it to AWS.

Set up billing alarms, it's what I do the first thing with any new AWS account (that, and setting up MFA!). Cloudformation template example here which creates a billing alarm.