Add support for an existing resource group to the build-image.ps1 script

[eduardkuijpers86]

Description

Adds support for an existing resource group to the build-image.ps1 script.

Useful for developers/teams that are blocked by Azure policies that can interfere with the image build or hosting(for example firewallShouldBeEnabledOnKeyVaultMonitoringEffect and deployazuremonitoringagentlinuxvms) and need to add policy exemptions on the resource group.

• Exposes the Packer variable build_resource_group_name in the build-image.ps1 script with parameter ExistingResourceGroupName
• Implements two parameter sets to ensure Packer variables build_resource_group_name, temp_resource_group_name, and location don't conflict as described in the Packer documentation on resource groups
• Added Write-output to show if Packer will be called with a temporary or existing resource group
• Added Pester tests to verify the parameter sets and that Packer is called using the correct variables
• Added the Pester tests as part of the GitHub workflow powershell-tests
• Updated docs on the Packer variables to better reflect the Packer documentation on resource groups

Test results

Temporary resource group

Build yaml:

Build output:

Resource group:

Existing resource group

Build yaml:

Build output:

Resource group:

Related issue:

N/A

Check list

• Related issue / work item is attached
• Tests are written (if applicable)
• Documentation is updated (if applicable)
• Changes are tested and related VM images are successfully generated

[Copilot]

Pull request overview

Adds support in the images.CI/linux-and-win/build-image.ps1 wrapper to run Packer builds in an existing Azure resource group, enabling teams to apply policy exemptions on that RG and avoid build-time policy blocks.

Changes:

• Added two PowerShell parameter sets to enforce Packer’s mutually-exclusive resource group options (temporary RG vs existing RG).
• Refactored Packer -var argument construction to a reusable helper and added logging indicating which RG mode is used.
• Added Pester tests for parameter sets and Packer invocation, and wired those tests into the powershell-tests workflow; updated docs for RG-related Packer variables.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
images.CI/linux-and-win/build-image.ps1	Adds ExistingResourceGroupName support and parameter-set-driven Packer var selection.
images.CI/linux-and-win/tests/build-image.Tests.ps1	Adds Pester tests validating parameter sets and correct Packer variables per mode.
.github/workflows/powershell-tests.yml	Runs the new linux-and-win Pester tests in CI and triggers the workflow on changes in that subtree.
docs/create-image-and-azure-resources.md	Updates documentation about RG-related Packer variables and their allowed combinations.