Terraform is able to import existing infrastructure. This allows you take resources you've created by some other means and bring it under Terraform management.
This is a great way to slowly transition infrastructure to Terraform, or to be able to be confident that you can use Terraform in the future if it potentially doesn't support every feature you need today.
» Currently State Only
The current implementation of Terraform import can only import resources into the state. It does not generate configuration. A future version of Terraform will also generate configuration.
Because of this, prior to running
terraform import it is necessary to write
resource configuration block for the resource, to which the
imported object will be mapped.
While this may seem tedious, it still gives Terraform users an avenue for importing existing resources. A future version of Terraform will fully generate configuration, significantly simplifying this process.