Terraform State
In the previous step, we changed the name argument of the Storage Account resource. Terraform then deleted the old Account and created a new one. However, how did Terraform know it can delete the old Account even though it wasn’t a part of our definition file anymore?
State file
In addition to creating resources in Azure, the terraform apply command has also created a terraform.tfstate file in the current directory. This file contains a snapshot of the most recently deployed infrastructure.
Terraform manages all the resources that are in the state file. In our case, the old Account was in the state file, but not in the definition, so Terraform deleted it. Terraform won’t touch any resources that you created outside of the current stack.
For more information on why Terraform requires state and why Terraform cannot function without the state, please see the page state purpose.
Checkpoint
Have a look at your .tfstate file. Then, you are good to go further :)