terraform plan shows missing vars errors. How to list all required variables before runnin plan? terraform validate shows "the configuration is valid"

When encountering missing variable errors during a Terraform plan, it's essential to ensure that all required variables are defined and populated correctly. If terraform validate indicates that the configuration is valid, but terraform plan throws errors about missing variables, it suggests that Terraform recognizes the structure but cannot ascertain the necessary input values for execution. Here’s how to manage and list required variables effectively prior to running a plan.

Understanding Required Variables in Terraform

Terraform utilizes input variables to customize configurations dynamically. Each module can declare variables that define how resources will be created. Some variables are required, meaning they must be provided values to proceed with operations like terraform plan.

Common Causes of Missing Variable Errors

1. Null or Undefined Variables: If you have not provided a value for required variables, Terraform will raise an error.
2. Incorrect Variable File Usage: Make sure your variable files (*.tfvars) are being properly referenced.
3. Dynamic Values: Issues can arise from dynamic variables if their expected formats are not adhered to.

How to List All Required Variables

To list all required variables before executing terraform plan, follow these steps:

1. Refer to the Variable Declarations

Inspect your variables.tf or equivalent files where variables are defined. Required variables are declared using the variable block without a default value:

variable "example_variable" {
  description = "An example required variable"
  type        = string
}

2. Using Terraform Console

You can run the Terraform Console to inspect variable definitions. Start the console with:

terraform console

Then, to list all defined variables, use:

var

This command will display all available variables along with their types.

3. Terraform Validate Command

Although terraform validate checks for syntactic correctness, it won’t list missing variables directly. However, running this command after any changes will help identify other potential issues.

4. Echo Required Variables

You can create a small script using bash or other scripting languages to echo required variables. For example, in bash:

terraform output -json | jq '.[].variables' | jq 'keys'

This assumes the variables are properly declared and organized, allowing you to see what is required.

5. Use .tfvars Files

Creating a variables file (e.g., terraform.tfvars) can help specify values for your required variables:

example_variable = "value"

Then, ensure you always call this file when executing Terraform commands:

terraform plan -var-file="terraform.tfvars"

6. Terraform Documentation and Module Metadata

Refer to the specific module documentation or metadata where applicable. Each module often provides guidelines on required inputs.

Conclusion

By systematically reviewing your variable declarations and utilizing Terraform's built-in tools such as the console and variable files, you can effectively anticipate and list all required variables. Doing so will mitigate errors during your terraform plan phase. Remember, while Terraform validation is essential, understanding variable requirements is crucial for seamless operations. If you continue to face issues, consider detailed error messages linked to variable definitions, which can provide additional insights into the configuration problems.