What is Terraform state?

Terraform state is the record Terraform keeps of what it manages. For every resource address in the configuration (aws_s3_bucket.logs, module.net.aws_vpc.main) it stores the ID of the real object and its attributes after the last apply. On each plan Terraform compares three things: the configuration, the state, and what the provider reads back from the real infrastructure.

Where it lives

• Local: terraform.tfstate in the working directory, the default. Fine for experiments only.
• Remote backend: an S3 bucket, Azure Storage container, Google Cloud Storage bucket, HCP Terraform and others. Remote state can be shared by a team and locked during operations so two applies cannot run at once.

terraform {
  backend "s3" {
    bucket       = "example-tf-state"
    key          = "prod/network.tfstate"
    region       = "eu-west-1"
    use_lockfile = true
  }
}

Rules of thumb

Drift is the difference between state and reality, for example a setting changed in the cloud console; terraform plan -refresh-only shows it.