How to Use Local Values in Terraform: Simple Guide

In Terraform, locals let you define named values that you can reuse within your configuration. You declare them inside a locals block and then reference them by name to keep your code clean and avoid repeating expressions.

Syntax

The locals block defines one or more local values as key-value pairs. Each key is a name you choose, and the value can be any valid Terraform expression. You reference these values elsewhere using local.name.

• locals block: Groups local values.
• key: The name of the local value.
• value: The expression or value assigned.
• reference: Use local.key to access the value.

terraform

locals {
  example_name = "Hello, Terraform!"
  example_number = 42
  example_list = ["a", "b", "c"]
}

output "greeting" {
  value = local.example_name
}

output "number" {
  value = local.example_number
}

output "letters" {
  value = local.example_list
}

Example

This example shows how to define local values for a project name and environment, then use them to build resource names. It demonstrates how locals help avoid repeating the same strings multiple times.

terraform

locals {
  project = "myapp"
  environment = "dev"
  resource_prefix = "${local.project}-${local.environment}"
}

resource "aws_s3_bucket" "example" {
  bucket = "${local.resource_prefix}-bucket"
  acl    = "private"
}

output "bucket_name" {
  value = aws_s3_bucket.example.bucket
}

Output

bucket_name = "myapp-dev-bucket"

Common Pitfalls

Common mistakes when using local values include:

• Trying to use local values outside the same module where they are defined.
• Using interpolation syntax ${} unnecessarily inside locals when not needed.
• Defining locals with complex expressions that are hard to read or debug.

Always keep local values simple and use them only within the module they are declared.

terraform

locals {
  # Wrong: unnecessary interpolation
  wrong_name = "myapp"

  # Right: simple string assignment
  right_name = "myapp"
}

output "wrong" {
  value = local.wrong_name
}

output "right" {
  value = local.right_name
}

Output

wrong = "myapp"
right = "myapp"

Quick Reference

Concept	Description	Example
Define locals	Use a locals block with key-value pairs	locals { name = "value" }
Reference locals	Use local.key to get the value	local.name
Scope	Locals are only available inside the module they are declared	Cannot access locals across modules
Use case	Avoid repeating expressions and improve readability	Build resource names from parts
Avoid	Unnecessary interpolation and complex logic	Use simple expressions

Key Takeaways

Use locals to define reusable values inside a Terraform module.

Reference local values with local.name to keep code clean and avoid repetition.

Locals are limited to the module where they are declared and cannot be shared across modules.

Avoid unnecessary interpolation syntax inside locals; assign values directly when possible.

Keep local values simple and readable to make your Terraform code easier to maintain.