78 lines
2.8 KiB
Plaintext
78 lines
2.8 KiB
Plaintext
---
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layout: docs
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page_title: Configuration Language
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sidebar_title: 'v1.5 Configuration Language'
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sidebar_current: configuration
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description: |-
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Packer uses text files to describe infrastructure and to set variables.
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These text files are called Packer _configurations_ and are
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written in the HCL language.
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---
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# HCL Configuration Language
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Packer uses the Hashicorp Configuration Language - HCL - designed to allow
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concise descriptions of the required steps to get to a build file. This page
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describes the features of HCL2 exhaustively, if you would like to give a quick
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try to HCL2, you can also read the quicker [HCL2 getting started
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guide](/guides/hcl).
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## Builds
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The main purpose of the HCL language is defining builds and sources. All other
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language features exist only to make the definition of builds more flexible and
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convenient.
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`packer build` takes one argument. When a directory is passed, all files in the
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folder with a name ending with ".pkr.hcl" or ".pkr.json" will be parsed using
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the HCL2 format. When a file ending with ".pkr.hcl" or ".pkr.json" is passed it
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will be parsed using the HCL2 schema. For every other case; the _JSON only_ old
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packer schema will be used.
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## Arguments, Blocks, and Expressions
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The syntax of the HCL language consists of only a few basic elements:
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```hcl
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source "amazon-ebs" "main" {
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ami_name = "main-ami"
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}
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<BLOCK TYPE> "<BLOCK LABEL>" "<BLOCK LABEL>" {
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# Block body
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<IDENTIFIER> = <EXPRESSION> # Argument
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}
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```
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- _Blocks_ are containers for other content and usually represent the
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configuration of some kind of object, like a source. Blocks have a
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_block type,_ can have zero or more _labels,_ and have a _body_ that contains
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any number of arguments and nested blocks. Most of Packer's features are
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controlled by top-level blocks in a configuration file.
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- _Arguments_ assign a value to a name. They appear within blocks.
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- _Expressions_ represent a value, either literally or by referencing and
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combining other values. They appear as values for arguments, or within other
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expressions.
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For full details about Packer's syntax, see:
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- [Configuration Syntax](./syntax.html)
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- [Expressions](./expressions.html)
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## Code Organization
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The HCL language uses configuration files that are named with the `.pkr.hcl`
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file extension. There is also [a JSON-based variant of the
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language](./syntax-json.html) that is named with the `.pkr.json` file
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extension.
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Configuration files must always use UTF-8 encoding, and by convention are
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usually maintained with Unix-style line endings (LF) rather than Windows-style
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line endings (CRLF), though both are accepted.
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## Configuration Ordering
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The ordering of root blocks is not significant. The order of `provisioner` or
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`post-processor` blocks within a `build` is the only major feature where block
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order matters.
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