60 lines
2.1 KiB
Markdown
60 lines
2.1 KiB
Markdown
---
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layout: "docs"
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page_title: "Configuring Local Values"
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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 Value Configuration
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Local values assign a name to an expression, that can then be used multiple
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times within a module.
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Comparing modules to functions in a traditional programming language,
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if [variables](./variables.html) are analogous to function arguments and
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[outputs](./outputs.html) are analogous to function return values then
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_local values_ are comparable to a function's local variables.
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This page assumes you're already familiar with
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[the configuration syntax](/docs/configuration/syntax.html).
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## Example
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Local values are defined in `locals` blocks:
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```hcl
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# Ids for multiple sets of EC2 instances, merged together
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locals {
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instance_ids = "${concat(aws_instance.blue.*.id, aws_instance.green.*.id)}"
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}
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# A computed default name prefix
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locals {
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default_name_prefix = "${var.project_name}-web"
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name_prefix = "${var.name_prefix != "" ? var.name_prefix : local.default_name_prefix}"
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}
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```
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## Description
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The `locals` block defines one or more local variables within a module.
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Each `locals` block can have as many locals as needed, and there can be any
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number of `locals` blocks within a module.
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The names given for the items in the `locals` block must be unique throughout
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a module. The given value can be any expression that is valid within
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the current module.
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The expression of a local value can refer to other locals, but as usual
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reference cycles are not allowed. That is, a local cannot refer to itself
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or to a variable that refers (directly or indirectly) back to it.
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It's recommended to group together logically-related local values into
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a single block, particulary if they depend on each other. This will help
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the reader understand the relationships between variables. Conversely,
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prefer to define _unrelated_ local values in _separate_ blocks, and consider
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annotating each block with a comment describing any context common to all
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of the enclosed locals.
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