Budgets (optional)

A free, opt-in module that creates a subscription-scoped monthly budget with email alerts. Disabled by default.

What it deploys

• 1 × Microsoft.Consumption/budgets (subscription scope, monthly grain)
• N notifications at the percent thresholds you configure (default: 50 %, 80 %, 100 %) on Actual spend
• 1 notification at 100 % of Forecasted spend, so you get warned before you actually overrun
• (Optional) Filter to a list of resource group names — empty means whole subscription

Cost: $0. Azure Cost Management is free.

Why opt-in?

• Budgets need at least one email recipient — there’s no sensible default.
• Many SMB customers already have org-wide cost alerts in Cost Management; deploying duplicates is noisy.
• Currency depends on the subscription’s billing profile; we don’t want to silently set USD for a EUR-billed sub.

Enable in Terraform

In your tfvars (or per-scenario file under infra/terraform/foundation/scenarios/):

# Existing scenario settings
scenario = "baseline"
location = "westcentralus"

# Enable the budget
budget_enabled      = true
budget_amount       = 200                                    # USD/EUR/etc per month
budget_alert_emails = ["platform@example.com", "finance@example.com"]
budget_thresholds   = [50, 80, 100]                          # percent of budget
# budget_resource_group_names = []                           # default: whole subscription

Plan + apply as normal:

terraform plan -var-file=scenarios/baseline.tfvars -var "subscription_id=$ARM_SUBSCRIPTION_ID"
terraform apply

The output budget_id returns the ARM resource ID (or null when disabled).

Enable in Bicep

In your *.bicepparam:

using '../main.bicep'

param scenario = 'baseline'
param location = 'westcentralus'

param budgetEnabled = true
param budgetAmount = 200
param budgetAlertEmails = [
  'platform@example.com'
  'finance@example.com'
]
param budgetThresholds = [
  50
  80
  100
]

Deploy:

az deployment sub create \
  --location <region> \
  --name foundation-baseline-with-budget \
  --parameters infra/bicep/foundation/scenarios/baseline.bicepparam

The output budgetId returns the ARM resource ID (empty string when disabled).

How alerts work

Trigger	When you get an email
Actual ≥ 50 %	When your billed month-to-date spend crosses 50 % of the budget
Actual ≥ 80 %	When billed spend crosses 80 %
Actual ≥ 100 %	When billed spend crosses 100 % (the budget is informational; Azure will not stop deployments)
Forecasted ≥ 100 %	When the projected end-of-month spend crosses 100 % — usually fires days before the actual breach

You can change the Actual thresholds by overriding budget_thresholds (TF) / budgetThresholds (Bicep). The Forecasted-100 % notification is always enabled.

Scoping to a subset of resource groups

If you only want to track spend for a specific workload (not the whole subscription), pass the RG names:

budget_resource_group_names = ["rg-spoke-prod-contoso-wcus"]

Bicep equivalent:

// Add to your bicepparam
param budgetResourceGroupNames = [
  'rg-spoke-prod-contoso-wcus'
]

Note: This is built into the Terraform variable surface today; the Bicep main currently exposes a sub-wide budget only. Add param budgetResourceGroupNames array = [] in main.bicep if you need RG scoping in Bicep — the underlying modules/budgets.bicep already supports it.

Validation rules

The Terraform module rejects invalid input at plan time:

• budget_amount must be > 0
• Each entry of budget_thresholds must be 1–1000
• Each entry of budget_alert_emails must look like an email address
• If budget_enabled = true, budget_alert_emails must contain at least one address (enforced via locals)

Bicep enforces @minValue(1) on budgetAmount and @minLength(1) on the budget module’s alertEmails parameter.

Tests

A *.tftest.hcl plan-mode test ships with the module:

cd infra/terraform/foundation
terraform test -filter=tests/budgets.tftest.hcl

It asserts:

• Default state (no budget_enabled) creates 0 budgets
• Enabling with valid emails creates 1 budget with the right amount + monthly grain

Removing the budget

Set budget_enabled = false (TF) or budgetEnabled = false (Bicep) and re-apply. The budget resource is destroyed; Cost Management retains historical spend data regardless.