Terraform Tutorial — What Are Data Sources?

Data sources are Terraform’s way of fetching information about resources that already exist — whether they were created by Terraform, by hand, or by another tool.

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Resource vs Data Source

Aspect	resource	data
Keyword	resource	data
Operation	Create, update, destroy	Read only
In state?	Yes — full lifecycle	Yes — as a reference
Changes infra?	Yes	No

# Resource: Terraform manages this VPC
resource "aws_vpc" "main" {
  cidr_block = "10.0.0.0/16"
}

# Data source: Terraform reads this VPC (created elsewhere)
data "aws_vpc" "existing" {
  id = "vpc-0abc123def456"
}

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When to Use Data Sources

Scenario	Example
Look up an AMI ID	Find the latest Amazon Linux 2023 AMI
Reference an existing VPC	Deploy into a VPC created by another team
Get availability zones	Dynamically get AZs for the current region
Read an IAM policy	Reference a managed AWS policy by name
Look up a Route53 zone	Get the zone ID for DNS record creation

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Data Source Syntax

data "PROVIDER_TYPE" "LOCAL_NAME" {
  # Arguments to filter/identify the resource
}

Access attributes with data.PROVIDER_TYPE.LOCAL_NAME.attribute:

data "aws_vpc" "main" {
  id = "vpc-0abc123"
}

resource "aws_subnet" "web" {
  vpc_id     = data.aws_vpc.main.id
  cidr_block = "10.0.1.0/24"
}

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Data Sources Are Refreshed Every Plan

Every time you run terraform plan or terraform apply, Terraform queries the API to get the latest data. This means data source values are always current.

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What’s Next?

Let’s dive deeper into the data block syntax and its attributes.

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← Data Sources Hub Data Source Syntax →