Terraform Module Troubleshooting Guide

#terraform #azure #infrastructureascode

Common Error: "Unsupported argument" or "Unsupported attribute."

Symptoms

Error: An argument named "variable_name" is not expected here
Error: This object does not have an attribute named "output_name"
These errors occur even when variables/outputs appear to be correctly defined

Root Causes & Solutions
1. Stale Terraform Module Cache (Most Common)
When you modify module variables or outputs, Terraform may use cached information.

Solution:

When to use: After ANY changes to:

Module variables (variables.tf)
Module outputs (outputs.tf)
Module source paths

2. Empty or Corrupted Files (Critical Issue)
Files may appear in your directory but contain 0 bytes of data.
How to check:

Look for files with Length: 0 or 0 bytes.
Solution: Recreate the file using command line to ensure it saves:

3. Missing Variable Definitions
Error indicates a variable that doesn't exist in the module's variables.tf.
Solution: Add the missing variable to modules/module_name/variables.tf:

Then clear cache and reinitialize (see Solution #1).

4. Missing Output Definitions
Module doesn't expose the output being referenced.
Solution: Add the output to modules/module_name/outputs.tf:

output "output_name" {
  description = "Description"
  value       = azurerm_resource.resource_name.id
}

Then clear cache and reinitialize.

Diagnostic Workflow
Step 1: Verify File Structure

Check for:

All required files exist
No files with 0 bytes
Correct directory structure

Step 2: Verify File Contents

Step 3: Clear Cache and Reinitialize

Step 4: Check Terraform Version

Example variables.tf:

variable "rg_name" {
  description = "Resource group name"
  type        = string
}

variable "location" {
  description = "Azure region"
  type        = string
}

Example outputs.tf:

output "resource_id" {
  description = "ID of the created resource"
  value       = azurerm_resource.name.id
}

Example module call in root main.tf:

module "example" {
  source   = "./modules/module_name"
  rg_name  = "my-rg"
  location = "eastus"
}

# Reference module output
resource "other_resource" "example" {
  dependency_id = module.example.resource_id
}

Common Mistakes to Avoid
❌ Don't: