Local Values

The Problem: Repeated Tag Definitions
Step 1: Define a locals Block
Step 2: Reference the Local Value
Step 3: Preview and Apply
Advanced Example: Combining Variables and Resource Attributes
When to Use Local Values
Further Reading and References

In this lesson, you’ll discover how to use local values (locals) in OpenTofu to eliminate duplication, improve readability, and keep your configuration DRY (Don’t Repeat Yourself).

The Problem: Repeated Tag Definitions

Imagine you have two AWS EC2 instances—web and db—that share identical tags. Without locals, your HCL might look like this:

resource "aws_instance" "web" {
  ami           = "ami-06178cf087598769c"
  instance_type = "t2.medium"

  tags = {
    Department = "finance"
    Project    = "cerberus"
  }
}

resource "aws_instance" "db" {
  ami           = "ami-0567cf08759818b"
  instance_type = "m5.large"

  tags = {
    Department = "finance"
    Project    = "cerberus"
  }
}

Defining the same tags in multiple resources increases maintenance overhead. Locals allow you to declare shared values in one place.

Step 1: Define a `locals` Block

Create a locals block to hold your common tag set:

locals {
  common_tags = {
    Department = "finance"
    Project    = "cerberus"
  }
}

Step 2: Reference the Local Value

Use local.common_tags within each resource:

resource "aws_instance" "web" {
  ami           = "ami-06178cf087598769c"
  instance_type = "t2.medium"

  tags = local.common_tags
}

resource "aws_instance" "db" {
  ami           = "ami-0567cf08759818b"
  instance_type = "m5.large"

  tags = local.common_tags
}

Step 3: Preview and Apply

Running tofu plan or tofu apply now shows both instances using the shared tags:

$ tofu apply
An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
  + create

OpenTofu will perform the following actions:

# aws_instance.db will be created
+ resource "aws_instance" "db" {
    + tags = {
        + "Department" = "finance"
        + "Project"    = "cerberus"
    }
}

# aws_instance.web will be created
+ resource "aws_instance" "web" {
    + tags = {
        + "Department" = "finance"
        + "Project"    = "cerberus"
    }
}

Plan: 2 to add, 0 to change, 0 to destroy.

Advanced Example: Combining Variables and Resource Attributes

Locals aren’t limited to static maps—they can also concatenate variables, resource attributes, and more. For instance, to generate a globally unique S3 bucket name:

variable "project" {
  description = "Name of the project"
  type        = string
  default     = "cerberus"
}

resource "random_string" "random_suffix" {
  length  = 6
  special = false
  upper   = false
}

locals {
  bucket_prefix = "${var.project}-${random_string.random_suffix.id}-bucket"
}

resource "aws_s3_bucket" "finance_bucket" {
  acl    = "private"
  bucket = local.bucket_prefix
}

When you run tofu apply, you’ll see:

$ tofu apply --auto-approve
random_string.random_suffix: Creating...
random_string.random_suffix: Creation complete after 0s [id=dhiabk]
aws_s3_bucket.finance_bucket: Creating...
aws_s3_bucket.finance_bucket: Creation complete after 0s [id=cerberus-dhiabk-bucket]
Apply complete! Resources: 2 added, 0 changed, 0 destroyed.

HCL supports both legacy interpolation ("${...}") and the newer direct syntax (var.project). Both work in locals, but be consistent across your codebase.

When to Use Local Values

Use Case	Local Value Example
Share common configuration across resources	`local.common_tags`
Build dynamic names or identifiers	`local.bucket_prefix`
Simplify complex expressions	Intermediate computed values

Watch Video

Demo OpenTofu Modules

Functions Operators and Conditional Expressions

Course Introduction

Introduction to Infrastructure as Code

OpenTofu Basics

OpenTofu State

Working with OpenTofu

Remote State

OpenTofu Provisioners

OpenTofu Import, Tainting Resources and Deubugging

OpenTofu Modules

OpenTofu Functions and Conditional Expressions

OpenTofu: Beyond Basics

Course Conclusion

Getting Started with OpenTofu

The Problem: Repeated Tag Definitions

Step 1: Define a `locals` Block

Step 2: Reference the Local Value

Step 3: Preview and Apply

Advanced Example: Combining Variables and Resource Attributes

When to Use Local Values

Further Reading and References

Watch Video

Course Introduction

Introduction to Infrastructure as Code

OpenTofu Basics

OpenTofu State

Working with OpenTofu

Remote State

OpenTofu Provisioners

OpenTofu Import, Tainting Resources and Deubugging

OpenTofu Modules

OpenTofu Functions and Conditional Expressions

OpenTofu: Beyond Basics

Course Conclusion

Getting Started with OpenTofu

Documentation Index

​The Problem: Repeated Tag Definitions

​Step 1: Define a locals Block

​Step 2: Reference the Local Value

​Step 3: Preview and Apply

​Advanced Example: Combining Variables and Resource Attributes

​When to Use Local Values

​Further Reading and References

Watch Video

The Problem: Repeated Tag Definitions

Step 1: Define a `locals` Block

Step 2: Reference the Local Value

Step 3: Preview and Apply

Advanced Example: Combining Variables and Resource Attributes

When to Use Local Values

Further Reading and References