ARM Templates vs Terraform
When adopting Infrastructure as Code (IaC) in Azure, two popular tools often come into play: Azure Resource Manager (ARM) Templates and Terraform. Both are powerful—but knowing their differences can help you decide which is right for your project.
What Are ARM Templates?
ARM Templates are JSON-based declarative files used to define and deploy Azure infrastructure in a repeatable, reliable way. They’re built and maintained by Microsoft and deeply integrated with Azure.
- Azure-native: Designed specifically for Azure environments.
- Idempotent: Running the same template multiple times yields the same result.
- Support for parameters, variables, and linked templates for dynamic deployments.
- Seamless integration with Azure features like RBAC, Policy, and Blueprints.
Example ARM Template (JSON):
{
"$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"resources": [
{
"type": "Microsoft.Storage/storageAccounts",
"apiVersion": "2022-09-01",
"name": "mystorageaccount",
"location": "eastus",
"properties": {}
}
]
}What Is Terraform?
Terraform is an open-source IaC tool by HashiCorp that uses its own declarative syntax (HCL) to define infrastructure. It supports multiple cloud providers—making it ideal for teams managing diverse environments.
- Multi-cloud support: Works with Azure, AWS, GCP, and more.
- Stateful: Tracks changes through state files.
- Highly modular with reusable
modules. - Offers
terraform planandapplyto preview and apply changes.
Example Terraform Code (HCL):
provider "azurerm" {
features {}
}
resource "azurerm_storage_account" "mystorage" {
name = "mystorageaccount"
location = "East US"
resource_group_name = "myResourceGroup"
account_tier = "Standard"
account_replication_type = "LRS"
}Key Differences: ARM Templates vs Terraform
| Feature | ARM Templates | Terraform |
|---|---|---|
| Scope | Azure-only | Multi-cloud (Azure, AWS, GCP) |
| Language | JSON | HCL (HashiCorp Configuration Language) |
| State Management | Managed by Azure | Uses local or remote .tfstate files |
| Modularity | Linked templates (less intuitive) | Built-in modules for reusability |
| Execution Plan | No preview (deploys immediately) | Provides a preview with terraform plan |
| Integration | Deep Azure integration (RBAC, Policy) | Requires external service connections |
When to Choose Which
-
Use ARM Templates if:
- You work entirely in the Azure ecosystem.
- You need native support for Azure security, governance, and compliance tools.
- Your team is comfortable working with JSON files.
-
Use Terraform if:
- You want to support multiple cloud platforms (AWS, GCP, etc.).
- You need modular, reusable infrastructure code with cleaner syntax.
- You require previewing changes and handling state explicitly.
Conclusion
Both ARM Templates and Terraform are valuable tools in the IaC toolkit. If you need deep Azure integration and compliance, ARM is a strong choice. For flexibility, modularity, and multi-cloud automation, Terraform often comes out on top.
Coming up next: how to use Azure DevOps to automate infrastructure deployments using these tools.