feat(bootstrap): expose move_subscriptions_to_target_management_group toggle (#4205)

[Shaik Naseeruddin (NaseerDevops-1994)]

Summary

Resolves #4205.

Exposes a new optional input move_subscriptions_to_target_management_group so that estates can opt out of relocating their platform subscriptions during bootstrap. Previously this was hardcoded to var.iac_type != "bicep-classic" with no way to override it, which forced subscription moves even for brownfield estates whose platform subscriptions are already placed in a management group hierarchy.

The input is added to all three VCS variants (azuredevops, github, local) and is fully backward-compatible: when left unset (null) the effective value is exactly today's behaviour.

Changes

• Add variable "move_subscriptions_to_target_management_group" (type = bool, default = null) to:

  • alz/azuredevops/variables.tf
  • alz/github/variables.tf
  • alz/local/variables.tf

• Wire it into each alz/<vcs>/main.tf when calling module "azure":

  move_subscriptions_to_target_management_group = var.move_subscriptions_to_target_management_group != null ? var.move_subscriptions_to_target_management_group : (var.iac_type != "bicep-classic")

  The pre-change expression (var.iac_type != "bicep-classic") remains the fallback, so unset = unchanged behaviour.

The consuming module input already exists (modules/azure/variables.tf) and gates the azapi_resource.subscription_placement for_each in modules/azure/subscription_placements.tf.

Usage (inputs.yaml)

No allowlist or schema change is required. The accelerator generates the bootstrap tfvars from the module's Terraform variables matched to inputs.yaml by name (Convert-HCLVariablesToInputConfig → Set-Config → Write-TfvarsJsonFile); the interactive-wizard schema (AcceleratorInputSchema.json) only enriches prompts and never gates values. Declaring the variable in alz/<vcs>/variables.tf (this PR) makes it settable directly:

# inputs.yaml
move_subscriptions_to_target_management_group: false

Left unset, behaviour is unchanged (true for Terraform/Bicep, false for bicep-classic).

Validation

• terraform fmt -check -recursive alz — clean.
• terraform init + terraform validate — "Success! The configuration is valid." for alz/local, alz/github, and alz/azuredevops.

Behavioural check (same brownfield Terraform estate, target_subscriptions = [management, connectivity, identity, security] — matching the issue's 4-subscription plan excerpt):

Scenario	iac_type	toggle	effective value	subscription placements
Default (unchanged)	terraform	unset	true	4
Brownfield opt-out	terraform	false	false	0
bicep-classic (unchanged)	bicep-classic	unset	false	0
Explicit opt-in	terraform	true	true	4

Setting the toggle to false cleanly drops the subscription placements to 0 (no subscriptions relocated), while the unset default preserves current behaviour.

Docs

A companion documentation update (migration guidance) will be raised separately in Azure/Azure-Landing-Zones and is intended to merge after this change is released.

[Shaik Naseeruddin (NaseerDevops-1994)]

Before / After — captured plan output

Behavioural proof of the toggle, using a self-contained harness that mirrors the exact expression in alz/<vcs>/main.tf and the for_each in modules/azure/subscription_placements.tf, with target_subscriptions = [management, connectivity, identity, security] (matching the issue's 4-subscription plan excerpt).

BEFORE (hardcoded — no opt-out possible)

Brownfield Terraform estate, original logic move = (iac_type != "bicep-classic"):

==================================================================
 BEFORE #4205  -  brownfield Terraform estate (subs ALREADY placed)
 Hardcoded: move = (iac_type != 'bicep-classic')  ->  no opt-out
==================================================================

  + effective_move_subscriptions = true
  + iac_type                     = "terraform"
  + subscription_placement_count = 4

^ subscriptions are FORCE-MOVED (count=4). No variable exists to prevent it.

AFTER (new toggle)

Same estate, move_subscriptions_to_target_management_group = false:

==================================================================
 AFTER #4205  -  same brownfield Terraform estate
 New: move_subscriptions_to_target_management_group = false
==================================================================

  + effective_move_subscriptions = false
  + iac_type                     = "terraform"
  + subscription_placement_count = 0
  + toggle_input                 = false

^ opt-out honoured (count=0). No subscriptions relocated.

--- regression check: defaults UNCHANGED when toggle is unset ---
  + effective_move_subscriptions = true
  + iac_type                     = "terraform"
  + subscription_placement_count = 4
^ terraform default still moves (count=4) - backward compatible.

Summary

Scenario	iac_type	toggle	subscription_placement
Before / default	terraform	unset	4
After (brownfield opt-out)	terraform	false	0
Regression (unset)	terraform	unset	4

Setting the toggle to false cleanly drops the subscription placements to 0 (no subscriptions relocated); leaving it unset preserves current behaviour. terraform validate also passes on all three variants (alz/local, alz/github, alz/azuredevops).

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