How to fix Error: Call to unknown function - There is no function named in Terraform

Run the following command to see which version of Terraform you have installed:

terraform version

Note the version number. Most commonly, this error occurs when your installed Terraform version is older than what your configuration requires.

Look for a terraform block in your configuration (usually in main.tf or a separate version file):

terraform {
  required_version = ">= 1.3"
}

If the required version is higher than what you have installed, that's your issue. Also check for required_providers blocks that might have version constraints.

If your installed version is older than required, upgrade Terraform:

On macOS (with Homebrew):

brew upgrade terraform

On Linux or manual installation:
1. Visit https://www.terraform.io/downloads.html
2. Download the appropriate binary for your system
3. Extract and move it to your PATH (e.g., /usr/local/bin)

Verify the upgrade:

terraform version

If you're upgrading Terraform, check the release notes for function changes. For example, in Terraform 1.3, the defaults function was removed.

Common deprecated functions:
- defaults() - removed in Terraform 1.3, use optional() with default values instead
- get_parent_tfvars_dir() - renamed to get_parent_terragrunt_dir() in Terragrunt 0.19+

Search your configuration for any functions matching the error message and check the Terraform documentation at https://developer.hashicorp.com/terraform/language/functions for the correct function name and syntax.

If you're using both Terraform and Terragrunt:

In regular Terraform files (.tf), use only Terraform built-in functions like:
- file(), filebase64(), jsonencode(), merge(), concat(), etc.

In Terragrunt files (terragrunt.hcl), you can use both Terraform functions AND Terragrunt-specific functions like:
- get_terragrunt_dir(), get_parent_terragrunt_dir(), path_relative_to_include(), etc.

If you're getting an unknown function error in a .tf file, make sure you're not using Terragrunt-specific functions there.

After upgrading or fixing function references, reinitialize Terraform:

# Remove the .terraform directory
rm -rf .terraform/

# Reinitialize Terraform
terraform init

Then retry your terraform plan or terraform apply command.