» Using the Isotime template function with a format string

The way you format isotime in golang is a bit nontraditional compared to how you may be used to formatting datetime strings.

Full docs and examples for the golang time formatting function can be found here

However, the formatting basics are worth describing here. From the golang docs:

These are predefined layouts for use in Time.Format and time.Parse. The reference time used in the layouts is the specific time:

Mon Jan 2 15:04:05 MST 2006

which is Unix time 1136239445. Since MST is GMT-0700, the reference time can be thought of as

01/02 03:04:05PM '06 -0700

To define your own format, write down what the reference time would look like formatted your way; see the values of constants like ANSIC, StampMicro or Kitchen for examples. The model is to demonstrate what the reference time looks like so that the Format and Parse methods can apply the same transformation to a general time value.

So what does that look like in a Packer template function?

{
    "variables":
    {
        "myvar": "packer-{{isotime \"2006-01-02 03:04:05\"}}"
    },
    "builders": [
        {
            "type": "null",
            "communicator": "none"
        }
    ],
    "provisioners": [
        {
            "type": "shell-local",
            "inline": ["echo {{ user `myvar`}}"]
        }
    ]
}

You can switch out the variables section above with the following examples to get different timestamps:

Date only, not time:

    "variables":
    {
        "myvar": "packer-{{isotime \"2006-01-02\"}}"
    },

A timestamp down to the millisecond:

    "variables":
    {
        "myvar": "packer-{{isotime \"Jan-_2-15:04:05.000\"}}"
    },

Or just the time as it would appear on a digital clock:

    "variables":
    {
        "myvar": "packer-{{isotime \"3:04PM\"}}"
    },