What is Terraform State

Terraform is a tool for building, changing, and versioning infrastructure. One of the core concepts of Terraform is the “state file,” which keeps track of the resources that Terraform manages.

The Terraform state file is a JSON file that stores the current state of the resources declared in your configuration files. The state file includes information about the resources’ attributes, dependencies, and metadata. When you run a Terraform command, Terraform reads the state file to determine the current state of the infrastructure.

The state file is stored locally by default, but it can also be stored remotely using backends like Amazon S3, Azure Blob Storage, or HashiCorp Consul. Storing the state file remotely makes it easier to collaborate with other team members and manage infrastructure changes.

Terraform uses the state file to determine what changes need to be made to bring the infrastructure into the desired state. When you apply changes to your configuration files, Terraform generates a new state file reflecting the new state of the infrastructure.

Terraform also uses the state file to ensure that the infrastructure remains in a consistent state. If the state file becomes out of sync with the actual infrastructure state, Terraform will detect the discrepancy and offer to fix it.

It’s important to treat the Terraform state file as a valuable asset, and to avoid editing it directly. Instead, use Terraform commands to make changes to the infrastructure, which will automatically update the state file.

Sometimes, you may have existing infrastructure resources that you want to manage with Terraform. In such cases, you can manually import these resources into your Terraform state file using the terraform import command.

Here are the general steps to import a resource:

1. Write a Terraform configuration file for the resource you want to import. This file should define the same provider, resource type, and attributes as the existing resource you want to import.
2. Run the terraform import command, passing in the provider, resource type, and identifier for the existing resource.

For example, let’s say you have an existing AWS EC2 instance with the ID i-0123456789abcdef. To import this resource into Terraform, you could create an aws_instance resource block in your configuration file like this:

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
}

Then, you could run the following command to import the existing instance into Terraform:

terraform import aws_instance.example i-0123456789abcdef

Note that the resource identifier (in this case, i-0123456789abcdef) may differ depending on the resource and provider you’re importing.

Once the resource is imported, Terraform will create a new state file entry for it, and you can manage it like any other Terraform-managed resource.

It’s important to note that not all resources can be imported into Terraform. The terraform import command relies on the provider’s ability to read and parse the existing resource’s configuration, so some resources may not be importable if the provider doesn’t support it.