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Configuration Templates

Certain configuration parameters within templates are themselves a type of "template." These are not Packer templates, but text templates, where variables can be used to modify the value of a configuration parameter during runtime.

For example, the ami_name configuration for the AMI builder is a template. An example value may be My Packer AMI {{.CreateTime}}. At runtime, this will be turned into My Packer AMI 1370900368, where the "CreateTime" variable was replaced with the Unix timestamp of when the AMI was actually created.

This sort of templating is pervasive throughout Packer. Instead of documenting the templating syntax in each location, it is documented once here so you know how to use it.

For advanced users: The templates are actually parsed and executed using Go's text/template package. It therefore supports the complete template syntax.

Syntax

99% of the time all you'll need within configuration templates are variables. Variables are accessed by using {{.VARIABLENAME}}. The "." prefixing the variable name signals that you're accessing a variable on the root template object. All template directives go between braces. Here is a piece of a VMware VMX template that uses variables:

.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"