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ARM vs Bicep vs Terraform decision in Azure - CLI Comparison

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Introduction
When you want to create and manage resources in Azure, you need a way to describe what you want. ARM templates, Bicep, and Terraform are tools that help you do this. Choosing the right one depends on your needs and comfort with each tool.
When you want to use a Microsoft-supported tool that works directly with Azure and prefer JSON format, use ARM templates.
When you want simpler, cleaner code than ARM templates but still want to stay within Azure's native tooling, use Bicep.
When you want to manage resources across multiple clouds or prefer a tool with a large community and simpler syntax, use Terraform.
When you want to reuse and share infrastructure code easily with others, Terraform offers modules and a big ecosystem.
When you want to avoid writing complex JSON and prefer a language that compiles to ARM templates, Bicep is a good choice.
Commands
This command deploys an ARM template named azuredeploy.json to the resource group example-rg. It shows how to apply ARM templates directly in Azure.
Terminal
az deployment group create --resource-group example-rg --template-file azuredeploy.json
Expected OutputExpected
{ "id": "/subscriptions/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/example-rg/providers/Microsoft.Resources/deployments/deployment1", "name": "deployment1", "properties": { "provisioningState": "Succeeded" } }
→
--resource-group - Specifies the Azure resource group to deploy to
→
--template-file - Specifies the ARM template file to use
This command compiles a Bicep file named main.bicep into an ARM template JSON file. It shows how Bicep simplifies writing infrastructure code by converting it to ARM JSON.
Terminal
bicep build main.bicep
Expected OutputExpected
The Bicep file main.bicep was successfully compiled to main.json
This command initializes a Terraform working directory. It downloads the Azure provider plugin and prepares Terraform to manage Azure resources.
Terminal
terraform init
Expected OutputExpected
Initializing the backend... Initializing provider plugins... - Finding latest version of hashicorp/azurerm... - Installing hashicorp/azurerm v3.0.0... - Installed hashicorp/azurerm v3.0.0 (signed by HashiCorp) Terraform has been successfully initialized!
This command applies the Terraform configuration to create or update Azure resources without asking for confirmation. It shows how Terraform manages infrastructure changes.
Terminal
terraform apply -auto-approve
Expected OutputExpected
azurerm_resource_group.example: Creating... azurerm_resource_group.example: Creation complete after 2s [id=/subscriptions/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/example-rg] Apply complete! Resources: 1 added, 0 changed, 0 destroyed.
→
-auto-approve - Skips interactive approval before applying changes
Key Concept

If you remember nothing else, remember: ARM templates are native but complex JSON, Bicep is simpler and compiles to ARM, and Terraform is cloud-agnostic with a friendly syntax.

Common Mistakes
Trying to write ARM templates directly without using Bicep or tools
ARM templates are complex JSON and hard to maintain by hand
Use Bicep to write simpler code that compiles to ARM templates
Using Terraform without initializing the directory first
Terraform needs to download providers and set up before applying changes
Always run 'terraform init' before 'terraform apply'
Mixing ARM template deployment commands with Terraform commands
They are different tools with different workflows and files
Choose one tool per project and follow its workflow consistently
Summary
Use 'az deployment group create' to deploy ARM templates directly to Azure.
Use 'bicep build' to convert Bicep files into ARM templates for simpler authoring.
Use 'terraform init' and 'terraform apply' to manage Azure resources with Terraform's cloud-agnostic approach.

Practice

(1/5)
1. Which tool is native to Azure and uses JSON for defining infrastructure?
easy
A. Terraform
B. Bicep
C. ARM templates
D. Ansible

Solution

  1. Step 1: Understand native Azure tools

    ARM templates are the original native infrastructure-as-code tool for Azure using JSON format.

  2. Step 2: Compare with other tools

    Bicep simplifies ARM but is not JSON; Terraform is multi-cloud and not native Azure.

  3. Final Answer:

    ARM templates -> Option C

  4. Quick Check:

    Native Azure tool with JSON = ARM templates [OK]
Hint: Native Azure + JSON = ARM templates [OK]
Common Mistakes:
  • Confusing Bicep as native JSON tool
  • Thinking Terraform is Azure native
  • Selecting Ansible which is not Azure native
2. Which syntax correctly declares a resource in Bicep?
easy
A. resource vm 'Microsoft.Compute/virtualMachines@2021-07-01' = { name: 'myVM' }
B.
C. resource "vm" { type = "Microsoft.Compute/virtualMachines" name = "myVM" }
D. vm_resource = { type: 'Microsoft.Compute/virtualMachines', name: 'myVM' }

Solution

  1. Step 1: Identify Bicep syntax

    Bicep uses the keyword 'resource' followed by a symbolic name, type with API version, and properties in braces.

  2. Step 2: Compare options

    resource vm 'Microsoft.Compute/virtualMachines@2021-07-01' = { name: 'myVM' } matches Bicep syntax; the XML-like syntax is invalid, the HCL-style block is Terraform syntax, and the plain object is invalid.

  3. Final Answer:

    resource vm 'Microsoft.Compute/virtualMachines@2021-07-01' = { name: 'myVM' } -> Option A

  4. Quick Check:

    Bicep resource syntax = resource vm 'Microsoft.Compute/virtualMachines@2021-07-01' = { name: 'myVM' } [OK]
Hint: Bicep uses 'resource name type@version = { }' syntax [OK]
Common Mistakes:
  • Choosing Terraform syntax for Bicep
  • Confusing ARM JSON/XML with Bicep
  • Using invalid assignment formats
3. Given this Terraform snippet:
resource "azurerm_resource_group" "rg" {
  name     = "example-rg"
  location = "eastus"
}

What will happen when you run terraform apply?
medium
A. Deletes existing resource groups in East US
B. Fails because 'azurerm_resource_group' is invalid
C. Creates a virtual machine instead of a resource group
D. Creates a resource group named 'example-rg' in East US

Solution

  1. Step 1: Understand Terraform resource block

    The block defines an Azure resource group named 'example-rg' in 'eastus' location.

  2. Step 2: Predict Terraform apply behavior

    Terraform will create the resource group if it doesn't exist, no deletion or VM creation occurs.

  3. Final Answer:

    Creates a resource group named 'example-rg' in East US -> Option D

  4. Quick Check:

    Terraform resource block creates defined resource [OK]
Hint: Terraform resource block creates specified resource [OK]
Common Mistakes:
  • Thinking resource type is invalid
  • Confusing resource group with VM
  • Assuming deletion happens automatically
4. You try to deploy an ARM template but get a syntax error. Which is the most likely cause?
medium
A. Missing resource group in Terraform provider
B. Using Bicep syntax directly in ARM JSON template
C. Incorrect API version in Bicep resource declaration
D. Using Terraform commands on ARM template

Solution

  1. Step 1: Identify syntax error source

    ARM templates require JSON syntax; using Bicep syntax directly causes errors.

  2. Step 2: Eliminate other options

    Missing resource group affects Terraform, not ARM JSON; API version errors in Bicep cause deployment errors but not syntax errors; Terraform commands on ARM templates cause command errors, not syntax errors.

  3. Final Answer:

    Using Bicep syntax directly in ARM JSON template -> Option B

  4. Quick Check:

    ARM JSON syntax error = Bicep syntax used wrongly [OK]
Hint: ARM templates need JSON, not Bicep syntax [OK]
Common Mistakes:
  • Mixing Bicep syntax in ARM JSON
  • Confusing deployment errors with syntax errors
  • Assuming Terraform errors affect ARM templates
5. Your company uses Azure and AWS. You want a single tool to manage infrastructure on both clouds with reusable code. Which tool should you choose?
hard
A. Terraform
B. Bicep
C. Azure CLI scripts
D. ARM templates

Solution

  1. Step 1: Identify multi-cloud support

    Terraform supports multiple cloud providers including Azure and AWS with reusable code modules.

  2. Step 2: Compare other tools

    ARM and Bicep are Azure-only; Azure CLI scripts are Azure-specific and not declarative infrastructure code.

  3. Final Answer:

    Terraform -> Option A

  4. Quick Check:

    Multi-cloud infrastructure tool = Terraform [OK]
Hint: Terraform works across clouds, ARM/Bicep only Azure [OK]
Common Mistakes:
  • Choosing ARM or Bicep for multi-cloud
  • Thinking Azure CLI manages AWS
  • Ignoring Terraform's multi-cloud strength