92 lines
2.7 KiB
Markdown
92 lines
2.7 KiB
Markdown
---
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layout: "docs"
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page_title: "Local Values - Configuration Language"
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sidebar_current: "docs-config-locals"
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description: |-
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Local values assign a name to an expression that can then be used multiple times
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within a module.
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---
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# Local Values
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-> **Note:** This page is about Terraform 0.12 and later. For Terraform 0.11 and
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earlier, see
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[0.11 Configuration Language: Local Values](../configuration-0-11/locals.html).
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A local value assigns a name to an [expression](./expressions.html),
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so you can use it multiple times within a module without repeating
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it.
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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](./variables.html) are like function arguments.
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- [Output values](./outputs.html) 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](./expressions.html) 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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