Environment Variables Overview

This Guide will describe two common ways on how to use environment variables with terraform. For more information you may check out the terraform docs directly.

Export or Directly Set During Terraform Command

This section will desribe how to pass in environment variables directly during the terraform command.

main.tf

// Create a variable which will be assigned during the command
variable "foo" {
  type = string
}

data "example_datasource" "all" {
  filter {
    // Reference that variable how you would normally in terraform 
    name = [var.foo]
  }
}

Using the above example, to set the environment variable for foo you must use the prefix of TF_VAR_ + the name of the variable i.e: TF_VAR_foo. This will translate to setting the variable during the command.

Example Command: TF_VAR_foo="example-name" terraform plan

or

Export and then run the terraform command

export TF_VAR_foo="example-name"

This will execute terraform plan with the value of example-name for the variable foo.

Using the External Terraform Provider

This section will describe how to use environment variables using the external terraform provider

env.sh

cat << EOF
{
 "foo": "test"
}
EOF

main.tf

terraform {
  required_providers {
    external = {
      source = "hashicorp/external"
      version = "2.3.4"
    }
  }
}

# Run the script to get the environment variables of interest.
# This is a datasource, so it will run at plan time.
data "external" "env" {
  program = ["bash", "env.sh"]
}

# Show the results of running the datasource. This is a map of environment
# variable names to their values.
output "env" {
  value = data.external.env.result
}

data "example_datasource" "all" {
  filter {
    name = [data.external.env.result["foo"]]
  }
}

In this example there are 2 files.

1. env.sh This creates the input for the environment variables you would like to pass into and use in the terraform configuration main.tf
2. main.tf this defines the external datasource which takes in the output from the external datasource and then it can be used in the example_datasource filter i.e data.external.env.result["foo"]