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113 lines
3.6 KiB
Plaintext
113 lines
3.6 KiB
Plaintext
---
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page_title: Local Values - HCL Configuration Language
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description: >-
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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 folder.
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---
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# Local Values
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`@include 'from-1.5/beta-hcl2-note.mdx'`
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There are two kinds of variables in HCL Packer templates: Input variables,
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sometimes simply called "variables", and Local variables, also known as
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"locals". Input variables may have defaults, but those defaults can
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be overridden from the command line or special variable files. Local variables
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can be thought of as constants, and are not able to be overridden at runtime.
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This page is about local variables. To learn about input variables, see the
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[input variables](/docs/templates/hcl_templates/variables) page.
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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 folder.
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If [variables](/docs/templates/hcl_templates/variables) are analogous to function arguments then
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_local values_ are comparable to a function's local variables.
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Input variable and local variable usage are introduced in the [_Variables
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Guide_](/guides/hcl/variables).
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## Examples
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Local values are defined in `local` or `locals` blocks:
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```hcl
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# Using the local block allows you to mark locals as sensitive, which will
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# filter their values from logs.
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local "mylocal" {
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expression = "${var.secret_api_key}"
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sensitive = true
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}
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# Using the locals block is more compact and efficient for declaring many locals
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# Ids for multiple sets of EC2 instances, merged together
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locals {
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instance_ids = "${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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# Local values can be interpolated elsewhere using the "local." prefix.
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source "virtualbox-iso" "example" {
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output = "${local.name_prefix}-files"
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# ...
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}
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```
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Named local maps can be merged with local maps to implement common or default
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values:
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```hcl
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# Define the common tags for all resources
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locals {
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common_tags = {
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Component = "awesome-app"
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Environment = "production"
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}
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}
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# Create a resource that blends the common tags with instance-specific tags.
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source "amazon-ebs" "server" {
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source_ami = "ami-123456"
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instance_type = "t2.micro"
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tags = "${merge(
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local.common_tags,
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map(
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"Name", "awesome-app-server",
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"Role", "server"
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)
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)}"
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# ...
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}
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```
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## Description
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The `local` block defines exactly one local variable within a folder. The block
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label is the name of the local, and the "expression" is the expression that
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should be evaluated to create the local. Using this block, you can optionally
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supply a "sensitive" boolean to mark the variable as sensitive and filter it
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from logs.
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The `locals` block defines one or more local variables within a folder.
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The names given for the items in the `locals` block must be unique throughout a
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folder. The given value can be any expression that is valid within the current
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folder.
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The expression of a local value can refer to other locals, but reference cycles
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are not allowed. That is, a local cannot refer to itself or to a variable that
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refers (directly or indirectly) back to it.
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It's recommended to group together logically-related local values into a single
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block, particularly if they depend on each other. This will help the reader
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understand the relationships between variables. Conversely, prefer to define
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_unrelated_ local values in _separate_ blocks, and consider annotating each
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block with a comment describing any context common to all of the enclosed
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locals.
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