90 lines
2.8 KiB
Plaintext
90 lines
2.8 KiB
Plaintext
---
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page_title: Local Values - Configuration Language
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description: >-
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Local values assign a name to an expression that can be used multiple times
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within a Terraform module.
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---
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# Local Values
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> **Hands-on:** Try the [Simplify Terraform Configuration with
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> Locals](https://learn.hashicorp.com/tutorials/terraform/locals?in=terraform/configuration-language&utm_source=WEBSITE&utm_medium=WEB_IO&utm_offer=ARTICLE_PAGE&utm_content=DOCS)
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> tutorial on HashiCorp Learn.
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A local value assigns a name to an [expression](/language/expressions),
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so you can use the name multiple times within a module without repeating
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the expression.
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If you're familiar with traditional programming languages, it can be useful to
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compare Terraform modules to function definitions:
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- [Input variables](/language/values/variables) are like function arguments.
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- [Output values](/language/values/outputs) are like function return values.
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- Local values are like a function's temporary local variables.
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-> **Note:** For brevity, local values are often referred to as just "locals"
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when the meaning is clear from context.
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## Declaring a Local Value
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A set of related local values can be declared together in a single `locals`
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block:
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```hcl
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locals {
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service_name = "forum"
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owner = "Community Team"
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}
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```
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The expressions in local values are not limited to literal constants; they can
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also reference other values in the module in order to transform or combine them,
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including variables, resource attributes, or other local values:
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```hcl
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locals {
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# Ids for multiple sets of EC2 instances, merged together
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instance_ids = concat(aws_instance.blue.*.id, aws_instance.green.*.id)
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}
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locals {
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# Common tags to be assigned to all resources
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common_tags = {
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Service = local.service_name
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Owner = local.owner
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}
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}
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```
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## Using Local Values
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Once a local value is declared, you can reference it in
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[expressions](/language/expressions) as `local.<NAME>`.
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-> **Note:** Local values are _created_ by a `locals` block (plural), but you
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_reference_ them as attributes on an object named `local` (singular). Make sure
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to leave off the "s" when referencing a local value!
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```
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resource "aws_instance" "example" {
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# ...
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tags = local.common_tags
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}
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```
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A local value can only be accessed in expressions within the module where it
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was declared.
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## When To Use Local Values
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Local values can be helpful to avoid repeating the same values or expressions
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multiple times in a configuration, but if overused they can also make a
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configuration hard to read by future maintainers by hiding the actual values
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used.
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Use local values only in moderation, in situations where a single value or
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result is used in many places _and_ that value is likely to be changed in
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future. The ability to easily change the value in a central place is the key
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advantage of local values.
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