Using auto.tfvars in Terraform

Overview

Terraform allows you to define variables in multiple ways, one of which is using .auto.tfvars files. These files automatically load variable values without explicitly specifying them in the Terraform command.

Benefits of Using auto.tfvars

• Automatic Loading: No need to pass -var-file when applying Terraform configurations.
• Consistent Naming: Standardized approach to defining variable values.
• Separation of Concerns: Keeps variable definitions separate from code, making it more readable and maintainable.

How auto.tfvars Works

Terraform automatically loads files ending with .auto.tfvars in the working directory when running terraform plan or terraform apply.

Example

1. Define Variables in variables.tf

variable "instance_type" {
  description = "Type of EC2 instance"
  type        = string
}
 
variable "instance_count" {
  description = "Number of instances to launch"
  type        = number
}

2. Create terraform.auto.tfvars

instance_type  = "t2.micro"
instance_count = 2

3. Apply Terraform Configuration

Run Terraform without specifying the variable file explicitly:

terraform init
terraform plan
terraform apply

Terraform automatically loads terraform.auto.tfvars and applies the values to the defined variables.

Naming Convention

Terraform loads all .auto.tfvars files in lexicographical order. If multiple files exist, they are merged, with later files overriding earlier values if duplicate variables exist.

Best Practices

• Use for Default Values: Ideal for defining default values that can be overridden if needed.
• Avoid Sensitive Data: Do not store secrets or credentials in .auto.tfvars. Use environment variables or terraform.tfvars instead.
• Git Ignore for Security: Consider adding *.auto.tfvars to .gitignore if it contains environment-specific configurations.

Conclusion

Using .auto.tfvars simplifies variable management in Terraform projects by automatically loading configurations, improving efficiency and maintainability.