KodeKloud Notes

Welcome to this lesson on using data sources in OpenTofu. Data sources let you read and reference existing infrastructure or local data, without creating or managing new resources.

Quiz Questions

Can a data source be used to create, update, and destroy infrastructure?
Answer: False. A data source only reads resource data and makes it available in OpenTofu.
For more details, see the official OpenTofu documentation.
Can a data source be created using the data block?
Answer: True. Data sources are defined with a data block, analogous to resource blocks.

Hands-On: Local File Data Source

In the directory /root/OpenTofu/project/lexcorp, update main.tf to:

Read the contents of /etc/os-release via the local_file data source.
Output that content as an OpenTofu output variable.

Incorrect Configuration

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

datasource "local_file" "os" {
  filename = "/etc/os-release"
}

Warning

The block keyword must be data, not datasource.
The output reference requires the data source name (os).

Corrected Configuration

data "local_file" "os" {
  filename = "/etc/os-release"
}

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

Apply the Configuration

opentofu init
opentofu plan
opentofu apply

Expected output:

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:
os-version = <<EOT
PRETTY_NAME="Ubuntu 22.04.3 LTS"
NAME="Ubuntu"
VERSION_ID="22.04"
...
EOT

AWS Data Sources

Next, we’ll work with AWS data sources. Below is a quick reference table for the examples covered.

AWS Data Source	Required Argument	Description
aws_ebs_volume	volume_id	Fetches the EBS volume ID
aws_s3_bucket	bucket	Specifies the existing bucket name

EBS Volume

Open ebs.tf to find a data source block for an AWS EBS volume:

data "aws_ebs_volume" "gpt_volume" {
  # configuration...
}

Question: Which attribute fetches the volume ID?
Answer: volume_id

S3 Bucket

In s3.tf, you’ll see a data source intended to read an existing S3 bucket:

data "aws_s3_bucket" "selected" {
  bucket_name = "bucket.test.com"
}

Warning

The argument bucket_name is invalid. The correct argument is bucket.

Correct configuration:

data "aws_s3_bucket" "selected" {
  bucket = "bucket.test.com"
}

That completes this lesson on OpenTofu data sources. In upcoming modules, you’ll get more hands-on practice with AWS data sources and resources. Happy building!

Demo Data Sources