terraform plan shows missing vars errors. How to list all required variables before runnin plan?

When working with Terraform, it's not uncommon to encounter errors related to missing required variables during the plan phase. Understanding how to identify and list these required variables before running a plan can save significant troubleshooting time. Here, we will explore how to efficiently list all required variables in your Terraform configuration.

Understanding Terraform Variables

In Terraform, variables allow users to customize configurations and manage dynamic input values for reusable modules. They can be defined in several ways, including assigning values directly in .tf files or through environment variables. When a required variable is not set, Terraform will throw errors during execution, making it crucial to ensure all necessary values are provided beforehand.

Steps to List Required Variables

1. Use terraform validate Command

The first step in identifying required variables is to validate the Terraform configuration. The terraform validate command checks whether the configuration is syntactically valid and also reveals any missing required variables.

terraform validate

This command will list errors, including those related to missing variables. Review the output to identify which variables need to be supplied.

2. Review Terraform Variable Definitions

Every variable in Terraform is defined with a variable block, which specifies the variable's name and its attributes. To see all required variables, you can manually review your .tf files (e.g., variables.tf) where variables are declared.

variable "example_var" {
  description = "An example variable"
  type        = string
  // No default implies it's required
}

Variables without a default value are mandatory. Ensuring that each of these variables is documented will help in creating a comprehensive list.

3. Using Terraform Commands with -json Output

For a programmatic approach, you can leverage Terraform's output in JSON format. By running the following command, you can obtain detailed information about your configuration, including variable requirements:

terraform plan -json

The output will contain a list of all inputs required for the plan. Parse through this JSON for references to any required variables.

4. Considering Module Variables

If your configuration uses modules, keep in mind that each module may also require its own set of variables. Ensure to check each module’s variables.tf as well to catch all necessary input parameters.

5. Using Terraform Variable Documentation

To further ease the process of keeping track of variables, consider documenting them thoroughly in separate documentation or using comments directly in the code. This practice ensures that anyone working with the Terraform codebase can quickly identify which variables are required and their respective purposes.

Best Practices

• Best Practice Documentation: Maintain clear documentation alongside the Terraform configurations, detailing all required variables and providing descriptions for each.
• Utilize .tfvars Files: Store variable values in .tfvars files to clearly delineate which variables are set. This enables cleaner organization and easy referencing when running plans.

Conclusion

By utilizing the terraform validate command, reviewing variable definitions, and leveraging JSON outputs, you can efficiently list all required variables for your Terraform configurations. Keeping a well-documented Terraform codebase, alongside best practices in variable management, will help mitigate the risk of running into missing variable errors during the plan phase. For ongoing projects, regularly revising your variable requirements and documentation can greatly enhance team collaboration and configuration management.