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In this lesson, you’ll learn how to leverage the locals block in Terragrunt to define reusable variables and expressions directly within your configuration. By centralizing complex values, you can simplify your HCL, reduce duplication, and improve maintainability.

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Benefits of the locals Block

Encapsulating expressions or static values into named local variables offers clear advantages:
BenefitDescription
Code readabilityImproves comprehension by giving meaningful names to expressions
Code reusabilityFollows DRY (Don’t Repeat Yourself) by reusing values in multiple places
The image is a diagram titled "Locals Block" highlighting two benefits: "Code readability" and "Code reusability."

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Considerations

Local variables are strictly confined to the configuration where they’re declared. They won’t be shared across sibling or parent Terragrunt files.
locals in Terragrunt are not global. You cannot reference a local variable defined in one directory from another unless explicitly passed through inputs or shared via a common config.
The image is a diagram titled "Locals Block" with two points: "Limited to the scope" and "Cannot be shared across configs," accompanied by icons. At the bottom, there's a label "Considerations."

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Best Practices

  • Group related expressions under a single locals block to keep your configuration tidy.
  • Name variables clearly to convey their purpose (e.g., project_name, environment_cidr).
  • Avoid overusing locals for trivial values; reserve them for expressions or values reused multiple times.
  • Document complex locals with inline comments for future maintainers.
The image is a slide titled "Locals Block" with a purple icon and text explaining it is used to reduce complexity by defining variables. It also includes a "Best Practices" button.

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Example Usage

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1. Defining a local variable

locals {
  project = "KodeKloud"
}

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2. Referencing locals from a shared config (common.hcl)

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

include "root" {
  path   = find_in_parent_folders()
  expose = true
}

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

inputs = {
  name = include.common.locals.project
}

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3. Adding file-specific locals

You can define additional locals in any Terragrunt file for values unique to that directory. 
locals {
  cidr = "10.100.0.0/16"
}

inputs = {
  name     = include.common.locals.project
  vpc_cidr = local.cidr
}
This cidr variable is available only within the current VPC configuration, ensuring isolation from other modules.

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