Terraform Platform Stack

Terraform Platform Stack Specialist

Overview

This skill provides expert guidance for Terraform infrastructure as code development in the Platform as a Service Stack v3.0.0+ environment. It focuses on deterministic patterns (MD5 naming, uuidv5 RBAC), feature flag orchestration, root-level module coordination, and strict adherence to platform anti-pattern rules.

When to Use This Skill

• Creating new Terraform modules for Platform Stack workloads
• Implementing feature flags with proper dependency validation
• Refactoring code to eliminate anti-patterns (random_string, null checks in count)
• Debugging "depends on resource attributes" errors
• Implementing RBAC with deterministic uuidv5() role assignments
• Adding time_sleep for RBAC propagation (180s delays)
• Orchestrating modules at root main.tf level (no inter-module dependencies)
• Validating Azure Provider 4.x compatibility (deprecated attributes)
• Troubleshooting RBAC propagation failures
• Optimizing Terraform state with boolean flags (not null checks)

MCP Integration

Canonical source: See agent's MCP Tool Usage Protocol. Always validate provider versions and resource schemas via MCP tools before any code generation.

Critical Platform Stack Standards

State Management (Azure Blob with Azure AD)

ALL projects use Azure Blob Storage with Azure AD authentication:

# backend.tf
terraform {
  backend "azurerm" {
    resource_group_name  = "rg-paas"
    storage_account_name = "storagepaas"
    container_name       = "tfstate"
    key                  = "platform.terraform.tfstate"  # Override per platform
    use_azuread_auth     = true  # MANDATORY (no access keys)
  }
}

Initialization (CLI):

terraform init \
  -backend-config="key=myplatform.terraform.tfstate" \
  -backend-config="use_azuread_auth=true"

Module Structure (Single Concern)

Standard module layout:

terraform/modules/{domain}/{resource}/
├── main.tf         # Resource + RBAC + network rules
├── variables.tf    # name, location, tags, managed_identity_principal_id
├── outputs.tf      # IDs, URIs, names (NO secret values)

Workloads include:

└── workloads/
    ├── observability/      # Log Analytics + App Insights
    ├── storage-account/    # RBAC-only storage
    ├── service-bus/        # Premium namespace
    ├── event-grid/         # Domain with subscriptions
    ├── sql/                # SQL Server + Database
    └── container-apps/     # Container Apps Environment
        # container-registry → external: tfmodules-as-a-service-stack

Root orchestration ONLY (terraform/main.tf):

module "storage" {
  count = var.enable_storage ? 1 : 0
  
  source                        = "./modules/workloads/storage-account"
  name                          = module.naming.storage_account
  location                      = var.location
  resource_group_name           = module.resource_group.name
  managed_identity_principal_id = var.enable_managed_identity ? module.managed_identity[0].principal_id : null
  vnet_subnet_ids               = var.enable_vnet ? [module.vnet_spoke[0].default_subnet_id] : []
  tags                          = var.tags
}

CRITICAL: Modules NEVER reference other modules - orchestration at root only!

Anti-Patterns

See terraform-platform-instructions.md — Anti-Pattern Detection section for the full grep validation workflow.

Count Conditions (Boolean Flags ONLY)

# ❌ WRONG - Causes "depends on resource attributes" error
count = var.log_analytics_workspace_id != null ? 1 : 0

# ✅ CORRECT - Use boolean flag
count = var.enable_observability ? 1 : 0

# Root main.tf passes workspace_id directly (not via count)
module "container_apps" {
  count = var.enable_container_apps ? 1 : 0
  
  log_analytics_workspace_id = var.enable_observability ? module.observability[0].workspace_id : null
}

Rule: Count conditions ONLY accept boolean variables. NO null checks, NO string comparisons.

Feature Flag Table

Container Registry Details:

• Source: External module from tfmodules-as-a-service-stack (git::https://github.com/orafaelferreiraa/tfmodules-as-a-service-stack.git//modules/azurerm_container_registry?ref=1.0.3)
• SKU: Controlled by container_registry_sku (string, default "Basic")
• RBAC: When enable_managed_identity = true, AcrPush + AcrPull roles are auto-assigned to the Managed Identity
• Container Apps Integration: When both enable_container_registry and enable_managed_identity are true, Container Apps receives MI pre-attached + ACR login_server
• Output: container_app_ready_config — composite zero-config output bundling MI + ACR login server for Container Apps

Deterministic Patterns

See terraform-platform-instructions.md for MD5 naming, uuidv5 RBAC, and 180s time_sleep patterns with ❌/✅ examples.

State Management (CRITICAL)

ALL projects use Azure Blob Storage remote state - NEVER local state

# backend.tf
terraform {
  backend "azurerm" {
    resource_group_name  = "rg-paas"
    storage_account_name = "storagepaas"
    container_name       = "tfstate"
    key                  = "<project>-<tenant>-<environment>.tfstate"

    # Credentials via environment variables:
    # ARM_SUBSCRIPTION_ID
    # ARM_TENANT_ID
    # ARM_CLIENT_ID
    # ARM_CLIENT_SECRET
  }
}

State file naming convention: <project>-<tenant>-<environment>.tfstate

Examples:

• aks-na-prod.tfstate
• network-stack-prod.tfstate
• workers-backend-sophie-dev.tfstate

State initialization:

terraform init -backend-config="key=<project>-<tenant>-<environment>.tfstate"

Multi-Tenant Configuration Architecture

Configuration layering (hub-and-spoke pattern):

project-root/
├── backend.tf
├── providers.tf
├── main.tf
├── variables.tf
├── cluster-config/
│   ├── common/
│   │   └── main.tfvars          # Base configuration for ALL tenants
│   └── specific/
│       ├── na/
│       │   ├── dev.tfvars       # NA dev overrides
│       │   ├── qa.tfvars        # NA qa overrides
│       │   └── prod.tfvars      # NA prod overrides
│       ├── sophie/
│       │   ├── dev.tfvars
│       │   └── prod.tfvars
│       └── woopi/
│           └── prod.tfvars
└── modules/
    └── <custom-modules>/

Usage pattern:

# Apply with layered configs
terraform plan \
  -var-file="cluster-config/common/main.tfvars" \
  -var-file="cluster-config/specific/na/prod.tfvars"

terraform apply \
  -var-file="cluster-config/common/main.tfvars" \
  -var-file="cluster-config/specific/na/prod.tfvars"

Variable naming for multi-tenant:

# Prefix tenant-specific variables
variable "na_subscription_id" {
  description = "North America subscription ID"
  type        = string
  sensitive   = true
}

variable "sophie_subscription_id" {
  description = "Sophie tenant subscription ID"
  type        = string
  sensitive   = true
}

# OR use maps for shared structure
variable "subscription_ids" {
  description = "Subscription IDs per tenant"
  type        = map(string)
  sensitive   = true

  default = {
    na     = ""
    sophie = ""
    woopi  = ""
  }
}

Version Constraints (CRITICAL)

ALWAYS pin versions with ~> constraint:

# versions.tf
terraform {
  required_version = ">= 1.9.0"

  required_providers {
    azurerm = {
      source  = "hashicorp/azurerm"
      version = "~> 4.57.0"    # Allows patch updates (4.57.x)
    }
    azuread = {
      source  = "hashicorp/azuread"
      version = "~> 3.1.0"
    }
    kubernetes = {
      source  = "hashicorp/kubernetes"
      version = "~> 2.31.0"
    }
  }
}

Version constraint rules:

• ✅ Use ~> 4.57.0 - allows patch updates (4.57.1, 4.57.2)
• ❌ NEVER use >= 3.0 - unpinned, breaks reproducibility
• ❌ NEVER use = 4.57.0 - exact pin, too restrictive
• ❌ NEVER omit version - breaks state compatibility

Before upgrading providers:

1. Check latest version: mcp_hashicorp_ter_get_latest_provider_version
2. Review CHANGELOG for breaking changes
3. Test in dev environment first
4. Update all modules to compatible versions

File Structure Standards

Standard project organization:

project-root/
├── backend.tf        # Remote state configuration
├── providers.tf      # Provider configurations with aliases
├── versions.tf       # Terraform and provider version constraints
├── variables.tf      # Input variable declarations
├── locals.tf         # Local values and computed variables
├── main.tf           # Primary resource definitions
├── network.tf        # Networking resources (optional)
├── outputs.tf        # Output declarations
├── *.tfvars          # Variable values (NOT in git if contains secrets)
└── modules/          # Local modules
    └── <module-name>/
        ├── main.tf
        ├── variables.tf
        ├── outputs.tf
        └── versions.tf

File-specific guidelines:

backend.tf:

terraform {
  backend "azurerm" {
    resource_group_name  = "rg-paas"
    storage_account_name = "storagepaas"
    container_name       = "tfstate"
    key                  = "will-be-overridden-at-runtime.tfstate"
  }
}

providers.tf:

terraform {
  required_version = ">= 1.9.0"

  required_providers {
    azurerm = {
      source  = "hashicorp/azurerm"
      version = "~> 4.57.0"
    }
  }
}

# Multiple provider configurations with aliases
provider "azurerm" {
  alias           = "stefanininam"
  subscription_id = var.stefanininam_subscription_id
  tenant_id       = var.stefanininam_tenant_id
  client_id       = var.stefanininam_client_id
  client_secret   = var.stefanininam_client_secret
  features {}
}

provider "azurerm" {
  alias           = "devops"
  subscription_id = var.devops_subscription_id
  tenant_id       = var.devops_tenant_id
  client_id       = var.devops_client_id
  client_secret   = var.devops_client_secret
  features {}
}

variables.tf:

variable "environment" {
  description = "Deployment environment"
  type        = string

  validation {
    condition     = contains(["dev", "qa", "prod"], var.environment)
    error_message = "Environment must be dev, qa, or prod."
  }
}

variable "tenant" {
  description = "Tenant identifier"
  type        = string

  validation {
    condition     = contains(["na", "sophie", "woopi", "dex"], var.tenant)
    error_message = "Tenant must be na, sophie, woopi, or dex."
  }
}

variable "client_secret" {
  description = "Azure service principal client secret"
  type        = string
  sensitive   = true  # ALWAYS mark secrets as sensitive
}

locals.tf:

locals {
  resource_prefix = "${var.tenant}-${var.environment}"

  common_tags = merge(
    var.tags,
    {
      Environment = var.environment
      Tenant      = var.tenant
      ManagedBy   = "Terraform"
      Project     = var.project_name
    }
  )

  location_short = {
    "East US"     = "eus"
    "West Europe" = "weu"
  }
}

outputs.tf:

# Output complete resource object
output "resource_group" {
  description = "Complete resource group object"
  value       = azurerm_resource_group.main
}

# Output specific attributes
output "resource_group_id" {
  description = "Resource group ID"
  value       = azurerm_resource_group.main.id
}

# Output JSON summary
output "resource_summary" {
  description = "JSON summary of key attributes"
  value = jsonencode({
    id       = azurerm_resource_group.main.id
    name     = azurerm_resource_group.main.name
    location = azurerm_resource_group.main.location
  })
}

# Sensitive outputs
output "connection_string" {
  description = "Database connection string"
  value       = azurerm_storage_account.main.primary_connection_string
  sensitive   = true  # ALWAYS mark secrets as sensitive
}

Module Development

See terraform-platform-instructions.md — Module Structure section. Standard layout: main.tf, variables.tf, outputs.tf with types, validation, and dual outputs (object + JSON).

Common Implementation Tasks

1. Creating New Resource Configuration

MCP workflow:

1. Get latest provider version: mcp_hashicorp_ter_get_latest_provider_version
2. Search for resource: mcp_hashicorp_ter_search_providers
3. Get resource details: mcp_hashicorp_ter_get_provider_details
4. Review workspace patterns: grep_search or semantic_search

Implementation:

# Variable declarations
variable "storage_account_replication" {
  description = "Storage account replication type"
  type        = string
  default     = "LRS"

  validation {
    condition     = contains(["LRS", "GRS", "RAGRS", "ZRS"], var.storage_account_replication)
    error_message = "Must be a valid replication type."
  }
}

# Resource with environment-specific logic
resource "azurerm_storage_account" "data" {
  provider                 = azurerm.stefanininam
  name                     = "st${var.tenant}${var.app_name}${var.environment}"
  resource_group_name      = azurerm_resource_group.main.name
  location                 = var.location
  account_tier             = "Standard"
  account_replication_type = var.environment == "prod" ? "GRS" : "LRS"

  # Dynamic configuration based on environment
  min_tls_version               = "TLS1_2"
  enable_https_traffic_only     = true
  allow_nested_items_to_be_public = false

  network_rules {
    default_action = var.environment == "prod" ? "Deny" : "Allow"
    ip_rules       = var.allowed_ips
    bypass         = ["AzureServices"]
  }

  tags = local.common_tags
}

# Outputs
output "storage_account_id" {
  description = "Storage account resource ID"
  value       = azurerm_storage_account.data.id
}

2. Debugging Terraform Issues

State Lock Issues:

Symptoms:

• "Error: Error locking state"
• "Error: state blob is already locked"

MCP workflow:

1. Search: "Terraform Azure blob storage state lock troubleshooting"

Resolution:

# Check blob lease status
az storage blob show `
  --account-name storagepaas `
  --container-name tfstate `
  --name <project>-<tenant>-<environment>.tfstate `
  --query "properties.lease" `
  --auth-mode login

# If lease is "locked", verify no one is running terraform
# Contact team to confirm

# Break lease (CAUTION)
az storage blob lease break `
  --blob-name <project>-<tenant>-<environment>.tfstate `
  --container-name tfstate `
  --account-name storagepaas `
  --auth-mode login

Plan Failures:

Symptoms:

• "Error: Unsupported argument"
• "Error: Invalid value for variable"
• "Error: Cycle" (circular dependency)

MCP workflow:

1. Get provider details for resource: mcp_hashicorp_ter_get_provider_details
2. Search docs: "Terraform "

Debugging steps:

# Enable detailed logging
export TF_LOG=DEBUG
export TF_LOG_PATH=terraform-debug.log
terraform plan

# Review log for specific error
grep -i "error" terraform-debug.log

# Visualize dependencies (for cycle errors)
terraform graph | dot -Tpng > graph.png

# Validate syntax
terraform validate

# Check provider versions
terraform version
terraform providers

Resource Already Exists:

Symptoms:

• "Error: A resource with the ID /subscriptions/... already exists"

Options:

Option 1: Import existing resource

# Get resource ID from Azure
az resource show --resource-group <rg> --name <name> --resource-type <type> --query id -o tsv

# Import into Terraform state
terraform import azurerm_resource_group.main "/subscriptions/<sub-id>/resourceGroups/<rg-name>"

# Verify import successful
terraform plan  # Should show no changes or only minor updates

Option 2: Remove from state (if recreating)

terraform state rm azurerm_resource_group.main

State Drift:

Symptoms:

• Terraform plan shows unexpected changes
• Manual changes were made in Azure Portal

Detection:

# Refresh state from actual resources
terraform refresh

# Detect drift
terraform plan -detailed-exitcode
# Exit code 0 = no changes
# Exit code 1 = error
# Exit code 2 = changes detected (drift)

# Show specific drift
terraform show

# For detailed diff
terraform plan -out=plan.tfplan
terraform show -json plan.tfplan | jq '.resource_changes'

Resolution:

# Option 1: Accept drift (update code to match reality)
# Modify .tf files to match current state

# Option 2: Force compliance (apply Terraform configuration)
terraform apply

# Option 3: Ignore specific attributes
resource "azurerm_resource_group" "main" {
  # ...

  lifecycle {
    ignore_changes = [
      tags["LastModified"],  # Ignore auto-updated tags
    ]
  }
}

3. State Management Operations

Migrating resources between states:

# Step 1: Remove from current state
terraform state rm azurerm_resource_group.example

# Step 2: Initialize new backend
terraform init -backend-config="key=new-project-na-prod.tfstate"

# Step 3: Import into new state
terraform import azurerm_resource_group.example "/subscriptions/<sub-id>/resourceGroups/<rg-name>"

# Step 4: Verify
terraform plan  # Should show no changes

Renaming resources in code:

# Move resource within same state (no Azure changes)
terraform state mv azurerm_resource_group.old_name azurerm_resource_group.new_name

# Update code to match
# In main.tf: change resource name from "old_name" to "new_name"

# Verify no changes planned
terraform plan

4. Testing and Validation

Pre-commit validation:

# Format all Terraform files
terraform fmt -recursive

# Validate syntax
terraform validate

# Check for security issues (if tfsec is installed)
tfsec .

# Validate provider versions
terraform version
terraform providers

# Generate documentation
terraform-docs markdown . > README.md