Terraform must store state about your managed infrastructure and configuration. This state is used by Terraform to map real world resources to your configuration, keep track of metadata, and to improve performance for large infrastructures.
This state is stored by default in a local file named "terraform.tfstate", but it can also be stored remotely, which works better in a team environment.
Terraform uses this local state to create plans and make changes to your infrastructure. Prior to any operation, Terraform does a refresh to update the state with the real infrastructure.
For more information on why Terraform requires state and why Terraform cannot function without state, please see the page state purpose.
» Inspection and Modification
While the format of the state files are just JSON, direct file editing of the state is discouraged. Terraform provides the terraform state command to perform basic modifications of the state using the CLI.
The CLI usage and output of the state commands is structured to be friendly for Unix tools such as grep, awk, etc. Additionally, the CLI insulates users from any format changes within the state itself. The Terraform project will keep the CLI working while the state format underneath it may shift.
Finally, the CLI manages backups for you automatically. If you make a mistake modifying your state, the state CLI will always have a backup available for you that you can restore.
The state is in JSON format and Terraform will promise backwards compatibility with the state file. The JSON format makes it easy to write tools around the state if you want or to modify it by hand in the case of a Terraform bug. The "version" field on the state contents allows us to transparently move the format forward if we make modifications.