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125 lines
4.0 KiB
125 lines
4.0 KiB
---
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page_title: Local variables
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description: >-
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The `local` and `locals` blocks define local variables that assign a name to an expression. Learn how to configure local variables.
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---
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# Local variables
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This topic provides reference information about the `local` and `locals` blocks, which define local variables that you can use in your Packer templates. To learn about input variables, refer to
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[Input variables](/packer/docs/templates/hcl_templates/variables).
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## Introduction
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Local variables assign a name to an expression, which you can use multiple
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times within a folder. The expression is evaluated at run time, and can
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reference input variables, other local variables, data sources, and HCL
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functions. You cannot overwrite local variables.
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Refer to [Input Variables and local variables](/packer/guides/hcl/variables) for additional information about variables in Packer.
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## Examples
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Local variables are defined in a `local` or `locals` block:
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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 variables can be referenced 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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{
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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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## Single `local` block
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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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```hcl
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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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```
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This block is also very useful for defining complex locals. Packer might take some time to expand and evaluate `locals`
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with complex expressions dependent on other locals. The `locals` block is read as a map. Maps are not sorted, and therefore
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the evaluation time is not deterministic.
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To avoid that, singular `local` blocks should be used instead. These will be
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evaluated in the order they are defined, and the evaluation order and time will always be the same.
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## `locals` block
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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 variables 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 variables 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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## Known limitations
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`@include 'datasources/local-dependency-limitation.mdx'`
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