5.5 KiB

Raw Blame History

layout	sidebar_current	page_title	description
docs	docs-templates-engine	Template Engine - Templates	All strings within templates are processed by a common Packer templating engine, where variables and functions can be used to modify the value of a configuration parameter at runtime.

Template Engine

All strings within templates are processed by a common Packer templating engine, where variables and functions can be used to modify the value of a configuration parameter at runtime.

For example, the {{timestamp}} function can be used in any string to generate the current timestamp. This is useful for configurations that require unique keys, such as AMI names. By setting the AMI name to something like My Packer AMI {{timestamp}}, the AMI name will be unique down to the second. If you need greater than one second granularity, you should use {{uuid}}, as when you have multiple builders in the same template.

In addition to globally available functions like timestamp shown before, some configurations have special local variables that are available only for that configuration. These are recognizable because they're prefixed by a period, such as {{.Name}}.

The complete syntax is covered in the next section, followed by a reference of globally available functions.

Syntax

The syntax of templates is extremely simple. Anything template related happens within double-braces: {{ }}. Variables are prefixed with a period and capitalized, such as {{.Variable}} and functions are just directly within the braces, such as {{timestamp}}.

Here is an example from the VMware VMX template that shows configuration templates in action:

.encoding = "UTF-8"
displayName = "{{ .Name }}"
guestOS = "{{ .GuestOS }}"

In this case, the "Name" and "GuestOS" variables will be replaced, potentially resulting in a VMX that looks like this:

.encoding = "UTF-8"
displayName = "packer"
guestOS = "otherlinux"

Global Functions

While some configuration settings have local variables specific to only that configuration, a set of functions are available globally for use in any string in Packer templates. These are listed below for reference.

build_name - The name of the build being run.
build_type - The type of the builder being used currently.
isotime [FORMAT] - UTC time, which can be formatted. See more examples below.
lower - Lowercases the string.
pwd - The working directory while executing Packer.
template_dir - The directory to the template for the build.
timestamp - The current Unix timestamp in UTC.
uuid - Returns a random UUID.
upper - Uppercases the string.

isotime Format

Formatting for the function isotime uses the magic reference date Mon Jan 2 15:04:05 -0700 MST 2006, which breaks down to the following:

	Day of Week	Month	Date	Hour	Minute	Second	Year	Timezone
Numeric	-	01	02	03 (15)	04	05	06	-0700
Textual	Monday (Mon)	January (Jan)	-	-	-	-	-	MST

The values in parentheses are the abbreviated, or 24-hour clock values

Note that "-0700" is always formatted into "+0000" because isotime is always UTC time.

Here are some example formated time, using the above format options:

isotime = June 7, 7:22:43pm 2014

{{isotime "2006-01-02"}} = 2014-06-07
{{isotime "Mon 1504"}} = Sat 1922
{{isotime "02-Jan-06 03\_04\_05"}} = 07-Jun-2014 07\_22\_43
{{isotime "Hour15Year200603"}} = Hour19Year201407

Please note that double quote characters need escaping inside of templates (in this case, on the ami_name value):

{
  "builders": [
    {
      "type": "amazon-ebs",
      "access_key": "...",
      "secret_key": "...",
      "region": "us-east-1",
      "source_ami": "ami-fce3c696",
      "instance_type": "t2.micro",
      "ssh_username": "ubuntu",
      "ami_name": "packer {{isotime \"2006-01-02\"}}"
    }
  ]
}

-> Note: See the Amazon builder documentation for more information on how to correctly configure the Amazon builder in this example.

Amazon Specific Functions

Specific to Amazon builders:

clean_ami_name - AMI names can only contain certain characters. This function will replace illegal characters with a '-" character. Example usage since ":" is not a legal AMI name is: {{isotime | clean_ami_name}}.

5.5 KiB Raw Blame History