terraform/website/docs/configuration-0-11/locals.html.md

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---
layout: "language"
page_title: "Local Values - 0.11 Configuration Language"
sidebar_current: "docs-conf-old-locals"
description: |-
Local values assign a name to an expression that can then be used multiple times
within a module.
---
# Local Values
-> **Note:** This page is about Terraform 0.11 and earlier. For Terraform 0.12
and later, see
[Configuration Language: Configuring Local Values](/docs/language/values/locals.html).
Local values assign a name to an expression, that can then be used multiple
times within a module.
Comparing modules to functions in a traditional programming language,
if [variables](./variables.html) are analogous to function arguments and
[outputs](./outputs.html) are analogous to function return values then
_local values_ are comparable to a function's local variables.
This page assumes you're already familiar with
[the configuration syntax](./syntax.html).
## Examples
Local values are defined in `locals` blocks:
```hcl
# Ids for multiple sets of EC2 instances, merged together
locals {
instance_ids = "${concat(aws_instance.blue.*.id, aws_instance.green.*.id)}"
}
# A computed default name prefix
locals {
default_name_prefix = "${var.project_name}-web"
name_prefix = "${var.name_prefix != "" ? var.name_prefix : local.default_name_prefix}"
}
# Local values can be interpolated elsewhere using the "local." prefix.
resource "aws_s3_bucket" "files" {
bucket = "${local.name_prefix}-files"
# ...
}
```
Named local maps can be merged with local maps to implement common or default
values:
```hcl
# Define the common tags for all resources
locals {
common_tags = {
Component = "awesome-app"
Environment = "production"
}
}
# Create a resource that blends the common tags with instance-specific tags.
resource "aws_instance" "server" {
ami = "ami-123456"
instance_type = "t2.micro"
tags = "${merge(
local.common_tags,
map(
"Name", "awesome-app-server",
"Role", "server"
)
)}"
}
```
## Description
The `locals` block defines one or more local variables within a module.
Each `locals` block can have as many locals as needed, and there can be any
number of `locals` blocks within a module.
The names given for the items in the `locals` block must be unique throughout
a module. The given value can be any expression that is valid within
the current module.
The expression of a local value can refer to other locals, but as usual
reference cycles are not allowed. That is, a local cannot refer to itself
or to a variable that refers (directly or indirectly) back to it.
It's recommended to group together logically-related local values into
a single block, particularly if they depend on each other. This will help
the reader understand the relationships between variables. Conversely,
prefer to define _unrelated_ local values in _separate_ blocks, and consider
annotating each block with a comment describing any context common to all
of the enclosed locals.