Getting an Environment Variable in Terraform Configuration

TLDR

To use environment variables in Terraform, you can pass them as input variables or use the TF_VAR_ prefix. Alternatively, use the env function to access environment variables directly in your configuration.

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Environment variables are a convenient way to pass dynamic values to Terraform configurations. This guide will show you how to retrieve and use environment variables effectively in Terraform.

Why Use Environment Variables?

• Dynamic Configurations: Pass values that change between environments (e.g., dev, staging, prod).
• Security: Store sensitive data like API keys or credentials securely.
• Automation: Simplify CI/CD pipelines by using environment variables for configuration.

Using Input Variables with TF_VAR_ Prefix

Terraform automatically maps environment variables with the TF_VAR_ prefix to input variables.

Example: Using TF_VAR_

Define an input variable in your configuration:

variable "region" {
  description = "The AWS region to deploy resources in."
  type        = string
}

Set the environment variable:

export TF_VAR_region=us-east-1

Run Terraform commands, and the region variable will automatically use the value from the environment variable.

Using the env Function

The env function allows you to access environment variables directly in your configuration.

Example: Using env

variable "api_key" {
  default = "${env("API_KEY")}" # Replace "API_KEY" with your environment variable name
}

output "api_key" {
  value = var.api_key
}

Set the environment variable:

export API_KEY=your-api-key

Run Terraform commands, and the api_key variable will use the value from the environment variable.

Best Practices

• Use Secure Storage: Store sensitive environment variables in a secure location, such as AWS Secrets Manager or HashiCorp Vault.
• Validate Inputs: Use validation blocks to enforce constraints on input variables.
• Document Variables: Clearly document which environment variables are required and their purpose.

By using environment variables in Terraform, you can create dynamic and secure configurations that adapt to different environments and workflows.