Flash card
AWS CloudFormation change sets: a reviewable diff between the running stack and a proposed template.
- Creating a change set computes the actions an update would take without executing any of them.
- Each change reports a Replacement value of True, False, or Conditional, which is where destructive updates become visible in advance.
- A change set can be inspected, approved, and only then executed, which is what makes it usable as a pipeline gate.
- Multiple change sets can exist against one stack at once, and creating one costs nothing.
- It predicts from the template and the resource types, so it reflects the declared change rather than anything happening outside CloudFormation.
Pick it when
Pick it when a scenario asks to see the effect of an update before applying it, particularly to catch a replacement that would destroy data. In a pipeline it is the natural approval point between build and deploy.
It's the wrong answer when
It is the wrong answer for finding out whether reality still matches the template, which is drift detection. Change sets compare the current template to a proposed one; drift compares the deployed resources to the template. Reaching for a change set to catch a console edit finds nothing.