Demystifying Terraform: Variables.tf vs Terraform.tfvars
Terraform, a powerful infrastructure-as-code tool, offers a plethora of features for managing your infrastructure. But amidst the plethora of configuration files, two often cause confusion: variables.tf and terraform.tfvars. This article aims to clarify the differences between these files and provide a comprehensive understanding of their purpose.
Understanding the Need for Variables
Let's imagine you're deploying a virtual machine (VM) to the cloud using Terraform. This VM requires details like its name, region, and instance type. Instead of hardcoding these values directly in your Terraform configuration files, it's much better to use variables. Variables allow you to:
- Reduce code repetition: Reuse the same configuration for multiple VMs with different values.
- Improve maintainability: Easily modify variables without altering the core Terraform code.
- Enhance security: Store sensitive information separately from your code, like passwords and API keys.
Variables.tf: The Variable Declaration
variables.tf is the file where you declare your Terraform variables. It acts as a blueprint, defining the name, type, and optional default value for each variable. Here's a simple example:
variable "instance_type" {
type = string
default = "t2.micro"
}
variable "region" {
type = string
default = "us-east-1"
}
In this example, we define two variables: instance_type and region. Both are of type string and have default values. This ensures that even if we don't provide values explicitly, Terraform will still have defaults to use.
Terraform.tfvars: Providing Variable Values
terraform.tfvars is where you supply the actual values for the variables declared in variables.tf. This file is separate from your main Terraform configuration, ensuring that sensitive data is not directly included in your code.
Here's an example of how to use terraform.tfvars to assign values to our variables:
instance_type = "t3.small"
region = "eu-west-1"
This terraform.tfvars file overrides the default values set in variables.tf.
Key Differences:
- Location:
variables.tfresides within your Terraform code, whileterraform.tfvarssits alongside your main configuration files. - Purpose:
variables.tfdeclares variables, defining their type and default values.terraform.tfvarsassigns specific values to these variables. - Security:
terraform.tfvarsis a good practice for storing sensitive data separately from the main configuration files.
Additional Tips
- Variable Scope: Variables declared in
variables.tfcan be used throughout your entire Terraform configuration. - Environment Variables: You can use environment variables to set values for your variables in
terraform.tfvarsusing the syntaxvar.environment_variable_name. - Multiple tfvars Files: You can have multiple
tfvarsfiles for different environments, likedev.tfvars,prod.tfvars, and use-var-fileflag during Terraform execution to specify the appropriate file.
Conclusion
Understanding the role of variables.tf and terraform.tfvars is crucial for effective Terraform management. By leveraging these files, you can create modular, flexible, and secure Terraform configurations. This practice promotes reusability, minimizes code duplication, and facilitates easy updates and deployments.
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