path relative to include

In this lesson, we’ll dive into Terragrunt’s path_relative_to_include function. This built-in helper calculates the relative path between the current .hcl file and the file specified in its include block. Use it to:

• Organize and modularize your configuration files
• Construct dynamic file paths
• Segregate remote state keys per module

Why Use path_relative_to_include?

Typical Terragrunt Setup

Imagine you have a shared common.hcl in a parent directory and multiple child modules that include it. You can tag each module’s remote state with its relative path:

terraform {
  source = "tfr://terraform-aws-modules/vpc/aws//?version=5.8.1"
}

locals {
  common_vars = read_terragrunt_config(
    find_in_parent_folders("common.hcl")
  )
}

include "common" {
  path = find_in_parent_folders("common.hcl")
}

inputs = {
  name = "${local.common_vars.inputs.project}-${local.common_vars.inputs.environment}"
  tags = {
    Path = path_relative_to_include()
  }
}

Here’s what happens when you run terragrunt plan:

Plan: 4 to add, 0 to change, 0 to destroy.

Changes to Outputs:
  + azs                                  = []
  + cgw_arns                             = []
  + cgw_ids                              = []
  + database_nat_gateway_route_ids       = []
  + database_route_table_association_ids = []
  + database_route_table_ids             = []
  + database_subnet_arns                 = []
  + database_subnets                     = []
  + database_subnets_cidr_blocks         = []
  + default_network_acl_id               = (known after apply)
  + default_route_table_id               = (known after apply)
  + default_security_group_id            = (known after apply)
  + elasticache_route_table_association_ids = []
  + elasticache_route_table_ids         = []
  + elasticache_subnet_arns             = []
  + elasticache_subnets                 = []

Notice how the Path tag reflects this module’s folder relative to common.hcl. By doing so, each module’s Terraform state is stored under a unique key in your remote backend, enhancing clarity and maintainability.

Further Reading

• Terragrunt Documentation on path_relative_to_include
• Terragrunt Remote State Configuration
• Terraform AWS VPC Module