feat: migrate Packer templates to HCL2 #7689

zachary-bailey · 2026-01-20T18:58:33Z

What this PR does / why we need it:

Migrates Packer template to HCL due to JSON deprecation and to make sure of additional Packer features

Which issue(s) this PR fixes:

JSON deprecation, reduces clutter and maintenance issues in the repo

Copilot

Pull request overview

This PR migrates Packer templates from JSON to HCL2 format to address JSON deprecation and leverage modern Packer features. The migration consolidates multiple distro-specific JSON templates into a unified HCL2 configuration with dynamic provisioners.

Changes:

Introduces new HCL2 configuration files (variables.pkr.hcl, source.pkr.hcl, build.pkr.hcl, packer-plugin.pkr.hcl) replacing multiple JSON templates
Updates build scripts to reference the new buildconfig directory structure
Refactors Makefile to use a single unified template path instead of multiple distro-specific paths

Reviewed changes

Copilot reviewed 9 out of 12 changed files in this pull request and generated 15 comments.

Show a summary per file

File	Description
vhdbuilder/packer/buildconfig/variables.pkr.hcl	Defines all Packer variables and local values with environment variable defaults
vhdbuilder/packer/buildconfig/source.pkr.hcl	Configures the Azure ARM builder source with image and infrastructure settings
vhdbuilder/packer/buildconfig/build.pkr.hcl	Defines the build process with dynamic provisioners for file uploads and shell scripts
vhdbuilder/packer/buildconfig/packer-plugin.pkr.hcl	Specifies required Packer plugin versions
vhdbuilder/packer/buildconfig/produce-packer-settings.sh	Script for generating Packer settings JSON from environment variables
vhdbuilder/packer/buildconfig/produce-packer-settings-functions.sh	Helper functions for settings generation and Azure resource management
vhdbuilder/packer/buildconfig/dynamic-provisioners/*.json	JSON files defining file upload/download mappings for different distros
packer.mk	Updated Makefile to use unified HCL2 template path instead of multiple JSON templates

Copilot · 2026-01-27T22:58:09Z

vhdbuilder/packer/buildconfig/source.pkr.hcl

+    buildNumber         = "${var.build_number}"
+    createdBy           = "aks-vhd-pipeline"
+    image_sku           = "${var.img_sku}"
+    now                 = "${var.create_time}"


The variable create_time is referenced but never declared. This will cause a Packer error. You need to add a variable declaration for create_time.

Copilot · 2026-01-27T22:58:10Z

vhdbuilder/packer/buildconfig/build.pkr.hcl

+    for_each = "${local.ubuntu_file_upload}"
+    content {
+      type        = "file"
+      source      = provisioner.value.source
+      destination = provisioner.value.destination
+      when        = lower(var.os_sku) == "ubuntu"
+    }
+  }
+
+  // AzureLinux-specific file uploads
+  dynamic "provisioner" {
+    for_each = "${local.azlinux_file_upload}"
+    content {
+      type        = "file"
+      source      = provisioner.value.source
+      destination = provisioner.value.destination
+      when        = lower(var.os_sku) == "cblmariner"
+    }
+  }
+
+  // Flatcar-specific file uploads
+  dynamic "provisioner" {
+    for_each = "${local.flatcar_file_upload}"
+    content {
+      type        = "file"
+      source      = provisioner.value.source
+      destination = provisioner.value.destination
+      when        = lower(var.os_sku) == "flatcar"


The when attribute is not valid for dynamic provisioners in Packer. The conditional logic should be implemented using a conditional expression in the for_each itself:

for_each = lower(var.os_sku) == "flatcar" ? local.flatcar_file_upload : []

Suggested change

for_each = "${local.ubuntu_file_upload}"

content {

type = "file"

source = provisioner.value.source

destination = provisioner.value.destination

when = lower(var.os_sku) == "ubuntu"

}

}

// AzureLinux-specific file uploads

dynamic "provisioner" {

for_each = "${local.azlinux_file_upload}"

content {

type = "file"

source = provisioner.value.source

destination = provisioner.value.destination

when = lower(var.os_sku) == "cblmariner"

}

}

// Flatcar-specific file uploads

dynamic "provisioner" {

for_each = "${local.flatcar_file_upload}"

content {

type = "file"

source = provisioner.value.source

destination = provisioner.value.destination

when = lower(var.os_sku) == "flatcar"

for_each = lower(var.os_sku) == "ubuntu" ? local.ubuntu_file_upload : []

content {

type = "file"

source = provisioner.value.source

destination = provisioner.value.destination

}

}

// AzureLinux-specific file uploads

dynamic "provisioner" {

for_each = lower(var.os_sku) == "cblmariner" ? local.azlinux_file_upload : []

content {

type = "file"

source = provisioner.value.source

destination = provisioner.value.destination

}

}

// Flatcar-specific file uploads

dynamic "provisioner" {

for_each = lower(var.os_sku) == "flatcar" ? local.flatcar_file_upload : []

content {

type = "file"

source = provisioner.value.source

destination = provisioner.value.destination

Copilot · 2026-01-27T22:58:10Z

vhdbuilder/packer/buildconfig/source.pkr.hcl

+
+  subscription_id                     = "${var.subscription_id}"
+  user_assigned_managed_identities    = "${var.msi_resource_strings}"
+  use_azure_cli_auth                  = "true"


The use_azure_cli_auth is set to the string "true" but should be a boolean value true (without quotes) or reference the variable var.use_azure_cli_auth. As defined in variables.pkr.hcl line 125, this variable is of type bool, so it should be referenced as:

use_azure_cli_auth = var.use_azure_cli_auth

Suggested change

use_azure_cli_auth = "true"

use_azure_cli_auth = var.use_azure_cli_auth

Copilot · 2026-01-27T22:58:10Z

vhdbuilder/packer/buildconfig/build.pkr.hcl

+    inline            = "${local.reboot_command}"
+    pause_after       = "60s"
+    skip_clean        = true
+  }
+
+  provisioner "shell" {
+    inline = ["/bin/bash -ux /home/packer/install-dependencies.sh"]
+    environment_vars = [
+      FEATURE_FLAGS=${var.feature_flags},
+      BUILD_NUMBER=${var.build_number},
+      BUILD_ID=${var.build_id},
+      COMMIT=${var.commit},
+      HYPERV_GENERATION=${var.hyperv_generation},
+      CONTAINER_RUNTIME=${var.container_runtime},
+      TELEPORTD_PLUGIN_DOWNLOAD_URL=${var.teleportd_plugin_download_url},
+      ENABLE_FIPS=${var.enable_fips},
+      IMG_SKU=${var.img_sku},
+      PRIVATE_PACKAGES_URL=${var.private_packages_url},
+      VHD_BUILD_TIMESTAMP=${local.vhd_build_timestamp}
+    ]
+  }
+
+  provisioner "shell" {
+    inline = ["sudo /bin/bash /home/packer/generate-disk-usage.sh"]
+  }
+
+  dynamic "provisioner" {
+    for_each = "${local.midway_file_downloads}"
+    content {
+      type        = "file"
+      direction   = "download"
+      source      = provisioner.value.source
+      destination = provisioner.value.destination
+    }
+  }
+
+  provisioner "shell" {
+    expect_disconnect = true
+    inline            = "${local.reboot_command}"


Unnecessary string interpolation. The expression "${local.reboot_command}" can be simplified to local.reboot_command since it's already a string value. The same simplification can be applied throughout this file where single values are wrapped in string interpolation without additional text.

Copilot · 2026-01-27T22:58:11Z

vhdbuilder/packer/buildconfig/source.pkr.hcl

+    image_version                         = "${var.captured_sig_version}"
+    replication_regions                   = ["${var.location}"]
+    resource_group                        = "${var.resource_group_name}"
+    subscription                          = "${local.gallery_subscription_id}"


The local variable gallery_subscription_id is referenced but never defined. This will cause a Packer error. You need to add a local or variable definition for gallery_subscription_id.

Copilot · 2026-01-27T22:58:13Z

vhdbuilder/packer/buildconfig/variables.pkr.hcl

+
+variable "captured_sig_version" {
+  type    = string
+  default = "${env("$${CAPTURED_SIG_VERSION")}"


The variable default value contains a malformed environment variable reference. The syntax "${env("$${CAPTURED_SIG_VERSION")}" has an extra dollar sign and brace. This should be "${env("CAPTURED_SIG_VERSION")}" to correctly reference the environment variable.

Suggested change

default = "${env("$${CAPTURED_SIG_VERSION")}"

default = "${env("CAPTURED_SIG_VERSION")}"

Copilot · 2026-01-27T22:58:13Z

vhdbuilder/packer/buildconfig/build.pkr.hcl

+      ENABLE_FIPS=${var.enable_fips},
+      IMG_SKU=${var.img_sku},
+      UA_TOKEN=${var.ua_token},
+      VHD_BUILD_TIMESTAMP=${local.vhd_build_timestamp}


The local variable vhd_build_timestamp is referenced but never defined in the variables.pkr.hcl file. This will cause a Packer error. You need to add a local or variable definition for vhd_build_timestamp.

Copilot · 2026-01-27T22:58:13Z

vhdbuilder/packer/buildconfig/variables.pkr.hcl

+
+variable "SkipLinuxAzSecPack" {
+  type    = string
+  default = true


The default value is set to the boolean true, but the type is declared as string. This type mismatch will cause a Packer error. The default should be "true" (string) or the type should be changed to bool.

Suggested change

default = true

default = "true"

Copilot · 2026-01-27T22:58:13Z

vhdbuilder/packer/buildconfig/variables.pkr.hcl

@@ -0,0 +1,265 @@
+locals {
+  // Managed Image settings - empty for ARM64 builds
+  managed_image_resource_group_name  = lower("${var.architecture}") == "arm64" ? "" : "${var.resource_group_name}"


The variable resource_group_name is referenced in line 3 but is never declared in this file. This will cause Packer to fail with an undefined variable error. You need to add a variable declaration for resource_group_name.

Copilot · 2026-01-27T22:58:14Z

packer.mk


 run-packer: az-login
-	@packer init ./vhdbuilder/packer/packer-plugin.pkr.hcl && packer version && ($(MAKE) -f packer.mk init-packer | tee packer-output) && ($(MAKE) -f packer.mk build-packer | tee -a packer-output)
+	@packer init ./vhdbuilder/packer/buildconfig/build.pkr.hcl && packer version && ($(MAKE) -f packer.mk init-packer | tee packer-output) && ($(MAKE) -f packer.mk build-packer | tee -a packer-output)


The packer init command should target the directory containing all HCL files (buildconfig) rather than just build.pkr.hcl. The correct command should be:

packer init ./vhdbuilder/packer/buildconfig

This ensures all .pkr.hcl files in the directory are properly initialized.

Suggested change

@packer init ./vhdbuilder/packer/buildconfig/build.pkr.hcl && packer version && ($(MAKE) -f packer.mk init-packer | tee packer-output) && ($(MAKE) -f packer.mk build-packer | tee -a packer-output)

@packer init ./vhdbuilder/packer/buildconfig && packer version && ($(MAKE) -f packer.mk init-packer | tee packer-output) && ($(MAKE) -f packer.mk build-packer | tee -a packer-output)

zachary-bailey added 30 commits January 15, 2026 13:32

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zachary-bailey added 20 commits January 16, 2026 14:40

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Merge branch 'main' into zb/migrateToHCL2

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zachary-bailey temporarily deployed to test January 20, 2026 18:59 — with GitHub Actions Inactive

Merge branch 'main' into zb/migrateToHCL2

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zachary-bailey temporarily deployed to test January 27, 2026 15:58 — with GitHub Actions Inactive

zachary-bailey added 2 commits January 27, 2026 14:49

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zachary-bailey temporarily deployed to test January 27, 2026 22:51 — with GitHub Actions Inactive

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feat: migrate Packer templates to HCL2 #7689

feat: migrate Packer templates to HCL2 #7689

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	use_azure_cli_auth = "true"
	use_azure_cli_auth = var.use_azure_cli_auth

	default = "${env("$${CAPTURED_SIG_VERSION")}"
	default = "${env("CAPTURED_SIG_VERSION")}"

	@packer init ./vhdbuilder/packer/buildconfig/build.pkr.hcl && packer version && ($(MAKE) -f packer.mk init-packer \| tee packer-output) && ($(MAKE) -f packer.mk build-packer \| tee -a packer-output)
	@packer init ./vhdbuilder/packer/buildconfig && packer version && ($(MAKE) -f packer.mk init-packer \| tee packer-output) && ($(MAKE) -f packer.mk build-packer \| tee -a packer-output)

feat: migrate Packer templates to HCL2 #7689

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Pull request overview

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zachary-bailey commented Jan 20, 2026 •

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