What is a Change Set in CloudFormation?

In AWS CloudFormation, a change set is a preview of proposed changes to a CloudFormation stack before those changes are actually applied. It allows users to assess the potential impact of updates on their running resources, such as whether resources will be created, modified, or deleted, before executing the change set.

what is At-least-once delivery

what is Exactly-once delivery

explain Dead Letter Queue

what is SNS Topic