Packer Vars Example

Or, why does it have to be this hard?

This repo was created to provide an example to illustrate my comments on this Github issue for @nywilken who so graciously offered to understand the use-case and possibly even address the difficulty of my use-case.

Use-case

Basically the use-case did the following, each with its own .pkr.hcl file. This process assumes an 'ova-builder` VM on VMware vCenter that will have been created by a different Packer template.

Step	Description
setup	Ensures the 'ova-builder` VM is running and the vCenter has required config.
clean	Ensures the VM is in a clean state, e.g. prior artifacts deleted.
app	Build a GoLang app on the VM.
iso	Builds a Linux ISO containing the GoLang App.
upload	Uploads the build ISO to a vCenter Datastore.
install	Installs the ISO to create a new 'App' VM on vCenter.
export	Exports the App VM back down to 'ova-builder' as an OVA file.
jfrog	Uploads the resulant OVA to jFrog Artifactory.

The above is even a simplification but is hopefully detailed enough to give a clear picture of the process.

Example

Aside from the code being proprietary and owned by a former client it would be far too complex to serve as a clarifying example, so I create the simplest example I could to illustrate the problem.

This example has two (2) steps: step1 and step2 and their respective Packer templates are ./step1/step1.pkr.hcl and ./step2/step2.pkr.hcl. The example also has a shared /vars.json which contains shared vars for logging into SSH and one var for each step, step1_var=foo and step2_var=bar, respectively.

All these steps do is they both use the null builder to reach into a Linux machine via SSH and then run an inline script echoing their variable's value.

Running the working example

To see this example work:

1. Make sure you have Packer installed (of course),
2. Clone this repo to a macOS or Linux machine.
3. Ensure you are in the working branch, which is the repo's default.
4. Change the ssh_* properties in ./vars.json to point to a host, user and password of a computer or VM you can SSH into, and then
5. Run make

The Problem

The problem is that Packer requires you to declare step2_var in ./step1/step1.pkr.hcl even though /step1/step1.pkr.hclnever references or otherwise usesstep2_var`, — as the following table illustrates:

Step	Packer Template	Template Uses property in ./vars.json	Template does NOT use:
step1	./step1/step1.pkr.hcl	step1_var=foo	step2_var
step2	./step2/step2.pkr.hcl	step2_var=bar	step1_var

Running the "warnings" example

To experience the problem this repo is trying to illustrate:

1. Make sure performed the steps for the working example first.
2. Checkout the warnings branch.
3. Run make

You should get the following output; notice the warnings:

packer build -force -var-file="./vars.json" "step1"
Warning: Undefined variable

A "step2_var" variable was set but was not found in known variables. To declare
variable "step2_var", place this block in one of your .pkr files, such as
variables.pkr.hcl


null.step2: output will be in this color.

==> null.step2: Using SSH communicator to connect: iso-builder.local
==> null.step2: Waiting for SSH to become available...
==> null.step2: Connected to SSH!
==> null.step2: Provisioning with shell script: /var/folders/fg/1dfmwyrx3wxbhj5lbdqpt7bw0000gn/T/packer-shell1383820945
    null.step2: We are running step 'foo'
Build 'null.step2' finished after 658 milliseconds 319 microseconds.

==> Wait completed after 658 milliseconds 394 microseconds

==> Builds finished. The artifacts of successful builds are:
--> null.step2: Did not export anything. This is the null builder
packer build -force -var-file="./vars.json" "step2"
Warning: Undefined variable

A "step1_var" variable was set but was not found in known variables. To declare
variable "step1_var", place this block in one of your .pkr files, such as
variables.pkr.hcl


null.step2: output will be in this color.

==> null.step2: Using SSH communicator to connect: iso-builder.local
==> null.step2: Waiting for SSH to become available...
==> null.step2: Connected to SSH!
==> null.step2: Provisioning with shell script: /var/folders/fg/1dfmwyrx3wxbhj5lbdqpt7bw0000gn/T/packer-shell2044896123
    null.step2: We are running step 'bar'
Build 'null.step2' finished after 373 milliseconds 507 microseconds.

==> Wait completed after 373 milliseconds 568 microseconds

==> Builds finished. The artifacts of successful builds are:
--> null.step2: Did not export anything. This is the null builder

The Desired Solution

Simply provide a command-line switch that will suppress those warnings.

Epilogue

I tested this in Packer 1.18.3 but I swear that earlier versions of Packer threw errors and failed to buiild instead of throwing warnings. Or at least that is what I remember.

So a warning is not as bad as an error, and if it never threw an error and always provided a warning then, as they say, my bad.

But still, a command-line switch to suppress would be much appreciated.