Terraform Tutorial · State and Workflow · Lesson 18 of 25

Terraform Data Sources

Data sources read information that exists outside your configuration, such as the latest AMI, the current account or an existing VPC, without managing it.

Reading existing things

A data block looks something up; it never creates or changes anything.

data "aws_ami" "ubuntu" {
  most_recent = true
  owners      = ["099720109477"] # Canonical
  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd-gp3/ubuntu-noble-24.04-amd64-server-*"]
  }
}

data "aws_caller_identity" "current" {}

resource "aws_instance" "web" {
  ami           = data.aws_ami.ubuntu.id
  instance_type = "t3.micro"
}

output "account_id" {
  value = data.aws_caller_identity.current.account_id
}

Refer to data sources as data.<type>.<name>.<attribute>.

A data source reading a file

terraform {
  required_providers {
    local = { source = "hashicorp/local", version = "~> 2.5" }
  }
}

resource "local_file" "source" {
  filename = "${path.module}/version.txt"
  content  = "2.4.1"
}

data "local_file" "version" {
  filename   = local_file.source.filename
  depends_on = [local_file.source]
}

output "version" {
  value = data.local_file.version.content
}

Output

Terraform will perform the following actions:

  # data.local_file.version will be read during apply
  # (depends on a resource or a module with changes pending)
 <= data "local_file" "version" {
      + content              = (known after apply)
      + content_base64       = (known after apply)
      + content_base64sha256 = (known after apply)
      + content_base64sha512 = (known after apply)
      + content_md5          = (known after apply)
      + content_sha1         = (known after apply)
      + content_sha256       = (known after apply)
      + content_sha512       = (known after apply)
      + filename             = "./version.txt"
      + id                   = (known after apply)
    }

  # local_file.source will be created
  + resource "local_file" "source" {
      + content              = "2.4.1"
      + content_base64sha256 = (known after apply)
      + content_base64sha512 = (known after apply)
      + content_md5          = (known after apply)
      + content_sha1         = (known after apply)
      + content_sha256       = (known after apply)
      + content_sha512       = (known after apply)
      + directory_permission = "0777"
      + file_permission      = "0777"
      + filename             = "./version.txt"
      + id                   = (known after apply)
    }

Plan: 1 to add, 0 to change, 0 to destroy.

Run this on your computer — see “Get Started” for setup.

Test yourself

Can a data source create infrastructure?

Yes
No

Show answer

Answer: No

Data sources only read. Use a resource to create something.