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Terraform

Load .env Variables into Terraform Script

By Filip on 10/05/2024

Learn how to securely manage and inject environment variables from a .env file into your Terraform scripts for streamlined infrastructure deployments.

Load .env Variables into Terraform Script

Table of Contents

Introduction

Terraform doesn't natively support reading .env files. However, you can work around this limitation using the local_exec provisioner. This involves creating a .env file with your environment variables and using a script to load these variables during the Terraform apply phase. Keep in mind that this method has limitations, as the variables won't be available during the plan phase. For accessing environment variables in your Terraform code, use the var. prefix. Alternatively, consider using Terraform variables defined in .tfvars files or input variables for improved management and portability.

Step-by-Step Guide

While Terraform doesn't directly support reading .env files, you can achieve this using a workaround. First, you'll need to have a .env file in your Terraform project's root directory. This file should contain key-value pairs for your environment variables, with each pair on a new line, separated by an equals sign (e.g., API_KEY=your_api_key).

Next, you can use the local_exec provisioner in your Terraform configuration to execute a command that reads the .env file and exports its contents as environment variables. You can use a command-line tool like source (for Unix-like systems) or dotenv (available in various programming languages) for this purpose.

For instance, you could add a null_resource block to your Terraform code that runs a script when your infrastructure is applied. This script would use source .env to load the environment variables.

However, keep in mind that this approach has limitations. The environment variables loaded this way will only be available during the Terraform apply phase, not during the plan phase. This means you won't see the actual values in your Terraform plan output.

For accessing environment variables within your Terraform configuration, you can use the var. prefix followed by the variable name (e.g., var.API_KEY). Terraform automatically looks for environment variables with the TF_VAR_ prefix, so if you have an environment variable named TF_VAR_API_KEY, you can access it in your Terraform code as var.API_KEY.

Remember that relying heavily on environment variables can make your Terraform code less portable and harder to manage. Consider using Terraform variables defined in variable definition files (.tfvars) or input variables for better control and documentation.

Code Example

This code snippet demonstrates two ways to use environment variables in Terraform. The first method utilizes a null_resource with a local-exec provisioner to load variables from a .env file during the apply phase. This approach, however, lacks plan-time visibility and portability. The second method leverages the TF_VAR_ prefix for environment variables, making them directly accessible in Terraform configurations. While convenient, using environment variables directly is generally discouraged in favor of .tfvars files or input variables for improved management, documentation, and portability.

1. .env file:

Create a .env file in your Terraform project's root directory:

API_KEY=your_api_key
DB_PASSWORD=your_db_password

2. Terraform configuration:

resource "null_resource" "load_env" {
  provisioner "local-exec" {
    command = "source .env && echo 'Environment variables loaded'"
  }
}

resource "aws_instance" "example" {
  # ... other resource configurations ...

  tags = {
    Name = "Example instance with API key: ${var.API_KEY}"
  }

  # ... other resource configurations ...

  depends_on = [null_resource.load_env]
}

Explanation:

  • null_resource: This resource doesn't create any actual infrastructure but allows us to run arbitrary commands.
  • local-exec provisioner: This provisioner executes the specified command on your local machine.
  • source .env: This command loads the environment variables from the .env file.
  • depends_on: This ensures that the aws_instance resource is created only after the environment variables are loaded.

Limitations:

  • Plan-time visibility: As mentioned earlier, the values from .env will only be available during the apply phase, not during the plan phase.
  • Portability: This approach might not be portable across different operating systems.

Using TF_VAR_ prefix:

1. Set environment variables:

export TF_VAR_API_KEY="your_api_key"
export TF_VAR_DB_PASSWORD="your_db_password"

2. Terraform configuration:

resource "aws_instance" "example" {
  # ... other resource configurations ...

  tags = {
    Name = "Example instance with API key: ${var.API_KEY}"
  }

  # ... other resource configurations ...
}

Explanation:

  • TF_VAR_ prefix: Terraform automatically recognizes environment variables with this prefix.
  • var.API_KEY: You can access the environment variable value using the var. prefix.

Recommendation:

While these workarounds can be helpful in specific situations, it's generally recommended to use Terraform variables defined in .tfvars files or input variables for better control, documentation, and portability.

Additional Notes

Security Considerations:

  • Avoid Sensitive Information in .env Files: Storing sensitive data like API keys and passwords directly in .env files is generally discouraged, especially if these files are version-controlled. Consider using secure secret management solutions like HashiCorp Vault or AWS Secrets Manager.
  • Environment Variables Can Be Insecure: Environment variables might be logged or exposed in system information, posing a security risk.

Alternative Approaches:

  • Terraform Cloud/Enterprise: These platforms offer built-in mechanisms for managing secrets and variables securely.
  • Configuration Management Tools: Tools like Ansible or Puppet can be used to inject secrets and configure environments before running Terraform.

Best Practices:

  • Use .tfvars for Non-Sensitive Data: Store non-sensitive configuration values in .tfvars files for better organization and readability.
  • Leverage Input Variables: Define input variables with clear descriptions and default values to make your Terraform modules reusable and easy to configure.
  • Document Variable Usage: Clearly document the purpose and expected format of all variables used in your Terraform code.

Additional Tips:

  • Use a Script to Load .env for Local Testing: You can create a simple script to load your .env file before running Terraform locally for testing purposes.
  • Explore Community Modules: The Terraform community offers modules that might provide more robust solutions for handling environment variables or integrating with secret management tools.

Remember: The best approach for managing environment variables and secrets in Terraform depends on your specific needs, security requirements, and workflow. Carefully evaluate different options and choose the one that best suits your project.

Summary

While not directly supported, you can load environment variables from a .env file in your Terraform project using a workaround:

Method:

  1. Create a .env file: Store key-value pairs in your project's root directory (e.g., API_KEY=your_api_key).
  2. Use local_exec provisioner: Execute a command (like source .env or using a tool like dotenv) within a resource like null_resource to load the variables during the apply phase.

Limitations:

  • Apply-time only: Variables are not available during the plan phase, making it difficult to preview their impact.
  • Portability and management: Over-reliance on environment variables can hinder code reusability and maintainability.

Alternatives:

  • Terraform variables: Define variables directly in your configuration or use variable definition files (.tfvars) for better control and documentation.
  • Input variables: Allow users to provide values during runtime.

Key takeaway: While possible, consider the limitations of using .env files and prioritize alternative approaches for managing environment variables in Terraform.

Conclusion

In conclusion, while Terraform doesn't directly support reading .env files, it's possible to achieve this using workarounds like the local_exec provisioner. However, these methods have limitations, particularly the lack of plan-time visibility and potential portability issues. For more robust and manageable solutions, consider using Terraform variables defined in .tfvars files or input variables. These approaches offer better control, documentation, and portability, making your infrastructure code more maintainable and scalable. Remember to prioritize security by avoiding sensitive information in .env files and exploring secure secret management solutions when necessary.

References

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