Azure ARM Templates | Declarative Deployments

You will deploy Azure resources from a parameterized ARM template and preview changes with what-if before applying. By the end you will run repeatable, idempotent deployments instead of one-off portal clicks.

Learning Objectives

Author an ARM template with parameters.
Preview changes with the what-if operation.
Deploy idempotently and confirm no drift on re-run.
Time: ~3 hours · Difficulty: Intermediate · Prereqs: the Azure CLI and a resource group.

Architecture Overview

Environment Setup

You will need: the Azure CLI and a target resource group.

Before you begin: always run what-if before deploying to production scopes.

Step-by-Step Execution

Write a parameterized template

# template.json (excerpt)
"parameters": { "saName": { "type": "string" } },
"resources": [{
  "type": "Microsoft.Storage/storageAccounts",
  "apiVersion": "2023-01-01",
  "name": "[parameters('saName')]",
  "location": "[resourceGroup().location]",
  "sku": { "name": "Standard_LRS" },
  "kind": "StorageV2"
}]

Preview with what-if

what-if shows exactly what will change before anything is created or modified.

az deployment group what-if -g tyf-rg --template-file template.json --parameters saName=tyfstore01

Deploy

$ az deployment group create -g tyf-rg --template-file template.json --parameters saName=tyfstore01

"provisioningState": "Succeeded"

Progress So Far

graph LR A[01 Template] -->|done| B[02 what-if] B -->|done| C[03 Deploy] style A fill:#1a4a1a,stroke:#00ff00,color:#fff style B fill:#1a4a1a,stroke:#00ff00,color:#fff style C fill:#1a4a1a,stroke:#00ff00,color:#fff

Testing & Validation

az deployment group what-if -g tyf-rg --template-file template.json --parameters saName=tyfstore01

Re-running what-if after a successful deploy should report no changes, proving the template is idempotent.

Troubleshooting

Name already taken: storage account names are globally unique; choose another.
Validation failed: run az deployment group validate to see the schema error.
Unexpected what-if changes: a property drifted in the portal; let the template be the source of truth.

Extension Ideas

Move to the cleaner Bicep syntax in Infrastructure as Code.
Deploy from a pipeline with GitHub Actions.
Audit deployed resources with CSPM.

Key Results

Deployed resources declaratively from a parameterized template.
Previewed every change with what-if before applying.
Confirmed idempotency: a re-run reported no changes.
Replaced manual portal steps with repeatable deployments.

Azure ARM Templates: Declarative, Idempotent Deployments