Terraform (AWS/GCP) Error: Invalid variable default value
Understanding Terraform and Its Purpose
Terraform is an open-source infrastructure as code (IaC) tool created by HashiCorp. It allows developers to define and provision data center infrastructure using a declarative configuration language. Terraform is widely used for managing cloud services such as AWS, GCP, and Azure, enabling efficient and repeatable infrastructure management.
Identifying the Symptom: Invalid Variable Default Value
When working with Terraform, you might encounter the error: Error: Invalid variable default value. This error typically arises during the execution of terraform plan or terraform apply commands. It indicates that there is a mismatch between the default value provided for a variable and the expected type or constraints of that variable.
Exploring the Issue: What Causes This Error?
The error occurs when the default value assigned to a variable in your Terraform configuration does not align with the variable's defined type. For instance, if a variable is expected to be a string, but the default value is a number, Terraform will raise this error. Similarly, if constraints such as validation rules are not met, the error will surface.
Common Scenarios Leading to This Error
- Type Mismatch: Assigning a number to a string variable or vice versa.
- Invalid List or Map: Providing a list or map that does not conform to the expected structure.
- Constraint Violation: Default value not meeting specified validation rules.
Steps to Resolve the Invalid Variable Default Value Error
To fix this error, follow these steps:
Step 1: Review the Variable Definition
Check the variable definition in your Terraform configuration file. Ensure that the type specified matches the type of the default value. For example:
variable "example_var" {
type = string
default = "default_value"
}
In this example, the default value is a string, which matches the variable type.
Step 2: Validate Constraints
If you have constraints defined using validation blocks, ensure that the default value satisfies these constraints. For example:
variable "example_var" {
type = string
default = "valid_value"
validation {
condition = length(var.example_var) > 5
error_message = "The value must be longer than 5 characters."
}
}
Ensure the default value "valid_value" meets the condition specified.
Step 3: Use Terraform Validate
Run terraform validate to check for syntax errors and validate the configuration. This command helps identify issues in the configuration files before applying changes.
terraform validate
Additional Resources
For more detailed information on Terraform variables, refer to the official Terraform documentation on variables. You can also explore the Terraform documentation for further guidance on configuration and best practices.
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