amazon web services - Is CloudFormation idempotent? -


i read in many places on internet cloudformation not idempotent, cannot find example proves fact.

could please provide me example runs resource prove cloudformation not idempotent ?

the definition of idempotent according wikipedia follows:

in computer science, term idempotent used more comprehensively describe operation produce same results if executed once or multiple times.

cloudformation considered not idempotent in several aspects of behavior:

  • calling create api stack exists result in error
  • calling update api unchanged cloudformation stack results in error
  • creating , deleting same stack again result in creating resources different arns iam users, security group ids, ec2 instance ids, vpc ids, etc...
  • resources modified outside of cloudformation not changed original values if existing stack updated existing content

however, high level 1 of main reasons use cloudformation represent infrastructure code can use produce same infrastructure repeatedly. identical original definition of idempotent, distinction on multiple times part here. listed above when using same stack , applying on top of or deleting stack , recreating it, technically not getting exact same results, practical standpoint understandable , acceptable.


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