68 lines
2.3 KiB
Markdown
68 lines
2.3 KiB
Markdown
---
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layout: "docs"
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page_title: "Configuration Templates"
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---
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# Configuration Templates
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All strings within templates are processed by a common Packer templating
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engine, where variables and functions can be used to modify the value of
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a configuration parameter at runtime.
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For example, the `{{timestamp}}` function can be used in any string to
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generate the current timestamp. This is useful for configurations that require
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unique keys, such as AMI names. By setting the AMI name to something like
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`My Packer AMI {{timestamp}}`, the AMI name will be unique down to the second.
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In addition to globally available functions like timestamp shown before,
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some configurations have special local variables that are available only
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for that configuration. These are recognizable because they're prefixed by
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a period, such as `{{.Name}}`.
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The complete syntax is covered in the next section, followed by a reference
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of globally available functions.
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## Syntax
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The syntax of templates is extremely simple. Anything template related
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happens within double-braces: `{{ }}`. Variables are prefixed with a period
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and capitalized, such as `{{.Variable}}` and functions are just directly
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within the braces, such as `{{timestamp}}`.
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Here is an example from the VMware VMX template that shows configuration
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templates in action:
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<pre>
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.encoding = "UTF-8"
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displayName = "{{ .Name }}"
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guestOS = "{{ .GuestOS }}"
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</pre>
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In this case, the "Name" and "GuestOS" variables will be replaced, potentially
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resulting in a VMX that looks like this:
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<pre>
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.encoding = "UTF-8"
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displayName = "packer"
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guestOS = "otherlinux"
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</pre>
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## Global Functions
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While some configuration settings have local variables specific to only that
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configuration, a set of functions are available globally for use in _any string_
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in Packer templates. These are listed below for reference.
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* `pwd` - The working directory while executing Packer.
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* `isotime` - UTC time in RFC-3339 format.
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* `timestamp` - The current Unix timestamp in UTC.
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* `uuid` - Returns a random UUID.
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## Amazon Specific Functions
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Specific to Amazon builders:
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* ``clean_ami_name`` - AMI names can only contain certain characters. This
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function will replace illegal characters with a '-" character. Example usage
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since ":" is not a legal AMI name is: `{{isotime | clean_ami_name}}`.
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