[gjhr]

OK but how does Terraform know you are renaming a resource? It is not a daemon always running and watching everything you type. It only gets a snapshot of your code to work from when you run it, it doesn't know what your code was before, just the saved state from your last run and the real state in your cloud provider. The only way it can track the state is through the name which you have provided it, if you change that name it cannot know without inferring something. Maybe it matches up all the attributes in your code and state and infers that a rename has happened. What happens when only 95% of attributes match? What happens when multiple things match (An ec2 instance only requires 2 attributes so this is plausible)?

Example 1:

You have 2 essentially identical EC2 VMs with terraform names vm1 and vm2. You decide these are not good descriptive names so change them to webserver1 and webserver2, before running that change you also realise you only need 1 of the servers so delete webserver2 from your code. Terraform runs a plan and sees there is now only a single VM definition but 2 VMs in state. Neither of the terraform identifiers match the original resources. How does it know which one was renamed and which one to delete?

Example 2:

You use Terraform for IaC and something like Chef for configuration management so your Terraform code exclusively deals with the "hardware". A service is being migrated to a new implementation so you need to delete the old VM and bring up a new one. Both old and new implementation have the same exact hardware requirements. You make the change in your Terraform code, deleting the old resource and creating a new one with the same requirements but a different name, and run a plan. Terraform tells you there's nothing to change because its inferred that you wanted to rename.