Data Sources

OpenTofu lets you provision infrastructure and reference attributes between resources using expressions. But what if a resource already exists—created manually, via another tool, or in a different configuration? Data sources solve this by fetching read-only information about existing infrastructure.

Why Use Data Sources?

Read attributes of existing resources without managing their lifecycle.
Integrate with resources created by CloudFormation, Ansible, Terraform, or manually.
Avoid duplicating state in multiple configurations.

Data sources are read-only. They cannot create, update, or destroy resources. For full lifecycle management, use resource blocks instead.

Referencing an Existing AWS Key Pair

Suppose you already have an AWS Key Pair named alpha. You can fetch its key_name for use in an EC2 instance:

data "aws_key_pair" "cerberus_key" {
  key_name = "alpha"
}

resource "aws_instance" "cerberus" {
  ami           = var.ami
  instance_type = var.instance_type
  key_name      = data.aws_key_pair.cerberus_key.key_name
}

data "aws_key_pair" "cerberus_key" declares a data source.
The argument key_name = "alpha" locates the existing key pair.
In the EC2 resource, data.aws_key_pair.cerberus_key.key_name provides the fetched value.

Check the AWS Provider Data Sources documentation for all available arguments and attributes: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/key_pair

Filtering Data Sources by Tags

When you can’t identify a resource by a single attribute, use filters. For example, locate the key pair tagged with project = cerberus:

data "aws_key_pair" "cerberus_key" {
  filter {
    name   = "tag:project"
    values = ["cerberus"]
  }
}

resource "aws_instance" "cerberus" {
  ami           = var.ami
  instance_type = var.instance_type
  key_name      = data.aws_key_pair.cerberus_key.key_name
}

The filter block matches key pairs with the given tag.
Multiple filters can be combined to narrow the search.

Resources vs. Data Sources

Aspect	Resource Blocks	Data Source Blocks
Lifecycle	Create, Read, Update, Delete	Read only
Keyword	`resource`	`data`
Terraform State	Managed	Not managed
Use Case	Provision infrastructure	Query existing infrastructure

Course Introduction

Introduction to Infrastructure as Code

OpenTofu Basics

OpenTofu State

Working with OpenTofu

Remote State

OpenTofu Provisioners

OpenTofu Import, Tainting Resources and Deubugging

OpenTofu Modules

OpenTofu Functions and Conditional Expressions

OpenTofu: Beyond Basics

Course Conclusion

Getting Started with OpenTofu

Why Use Data Sources?

Referencing an Existing AWS Key Pair

Filtering Data Sources by Tags

Resources vs. Data Sources

Links and References

Watch Video

​Why Use Data Sources?

​Referencing an Existing AWS Key Pair

​Filtering Data Sources by Tags

​Resources vs. Data Sources

​Links and References

Watch Video

Why Use Data Sources?

Referencing an Existing AWS Key Pair

Filtering Data Sources by Tags

Resources vs. Data Sources

Links and References