ARM vs Bicep vs Terraform decision in Azure - When to Use Which

The Big Idea

What if you could build your entire cloud setup with just one file and a single command?

The Scenario

Imagine you need to set up many cloud resources by clicking through a web portal one by one. Each time you want to make a change, you repeat the clicks. This takes hours and is easy to forget steps.

The Problem

Manual setup is slow and mistakes happen often. If you miss a step or type wrong, your cloud won't work right. Fixing errors means starting over or hunting for problems, wasting time and causing frustration.

The Solution

Using ARM, Bicep, or Terraform lets you write simple files that describe your cloud setup. You run these files to create or update resources automatically. This saves time, reduces errors, and makes changes easy and repeatable.

Before vs After

✗ Before

Click portal > Create VM > Set network > Repeat for each resource

✓ After

terraform apply
or
az deployment group create --template-file main.bicep

What It Enables

You can build, change, and share your cloud setup quickly and reliably without clicking or guessing.

Real Life Example

A company launches a new app and needs servers, databases, and networks. Using Terraform, they write one file to create all resources at once, then update it easily when the app grows.

Key Takeaways

Manual cloud setup is slow and error-prone.

ARM, Bicep, and Terraform automate resource creation with code.

This makes cloud management faster, safer, and repeatable.

Practice

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