Automate deployment of resources using ARM templates or Bicep

📘Microsoft Certified: Azure Administrator Associate (AZ-104)

When working as an Azure Administrator, you will often receive an existing ARM template or Bicep file that already deploys resources. Your job may be to update, extend, or fix these templates to meet new business requirements. The AZ-104 exam expects you to understand how to read, edit, and validate both ARM JSON templates and Bicep files.

1. Why You Need to Modify Existing Templates

Organizations use Infrastructure as Code (IaC) to deploy resources consistently. Over time, requirements change. For example, an existing template might need:

A new storage account added
A virtual machine size updated
Additional tags for cost management
A parameter renamed or made secure
A resource removed or replaced
A module added for better structure

The exam tests your ability to identify what part of the template must be changed and understand how those changes affect deployment.

2. Understanding the Structure Before Modifying

To modify a template, you must understand the basic structure.

ARM Template Structure (JSON)

ARM templates have these core sections:

Section	Purpose
$schema	Points to the JSON schema for template validation
contentVersion	Tracks version of the template
parameters	Values you can pass during deployment
variables	Reusable values defined inside the template
resources	Actual Azure resources defined in the template
outputs	Values returned after deployment

Bicep Structure

Bicep is simpler and cleaner:

param → parameters
var → variables
resource → resources
output → outputs

Example Bicep resource:

resource stg 'Microsoft.Storage/storageAccounts@2023-01-01' = {
  name: storageName
  location: location
  sku: {
    name: 'Standard_LRS'
  }
  kind: 'StorageV2'
}

3. Common Modifications You Must Know for the AZ-104 Exam

Below are the most exam-relevant updates you may need to perform.

A. Modify Parameters

1. Add a new parameter

Useful when you want flexibility.

Before

"parameters": {
  "location": {
    "type": "string"
  }
}

After (added new parameter)

"parameters": {
  "location": {
    "type": "string"
  },
  "storageSku": {
    "type": "string",
    "defaultValue": "Standard_LRS"
  }
}

2. Change a parameter to a secure parameter

Often used for secrets, passwords, connection strings.

"adminPassword": {
  "type": "secureString"
}

Bicep:

param adminPassword securestring

B. Modify Variables

Example: Add a variable for resource naming

var vmName = '${env}-web-vm'

Variables help maintain consistency and reduce repeated code.

C. Modify Resources

This is the most important section for the exam.

You may need to:

1. Change SKU or size

Example: VM size change

Bicep:

hardwareProfile: {
  vmSize: 'Standard_DS2_v2'
}

2. Add or remove properties

Example: Adding tags

tags: {
  environment: 'production'
  owner: 'IT'
}

3. Add a completely new resource

For example, adding a network security group (NSG) to a VNet template:

resource nsg 'Microsoft.Network/networkSecurityGroups@2023-05-01' = {
  name: 'web-nsg'
  location: location
}

4. Modify dependencies

Some resources depend on others.

In ARM:

"dependsOn": [
  "[resourceId('Microsoft.Network/virtualNetworks', 'myVnet')]"
]

In Bicep, this is automatic, but you can explicitly declare:

resource vm 'Microsoft.Compute/virtualMachines@2023-07-01' = {
  name: 'myVM'
  dependsOn: [ nsg ]
}

D. Update Outputs

Useful for retrieving details after deployment, such as:

Storage account name
Public IP address

Example:

output publicIpAddress string = publicIp.properties.ipAddress

4. Converting Between ARM and Bicep During Modification

You may receive an ARM template but want to convert it to Bicep to make modifications easier.

Decompile ARM → Bicep

bicep decompile azuredeploy.json

Build Bicep → ARM

bicep build main.bicep

5. Validating Changes Before Deployment

Azure provides tools to check templates after modifications.

A. Validate using Azure CLI

az deployment group validate \
  --resource-group RG1 \
  --template-file main.bicep

B. Validate using PowerShell

Test-AzResourceGroupDeployment -ResourceGroupName RG1 -TemplateFile main.bicep

C. Use VS Code Bicep/ARM extensions for linting

These tools highlight:

syntax errors
missing properties
wrong API versions
invalid resource types

6. Testing Modified Templates

After updating the template, deploy it in a test environment:

Azure CLI:

az deployment group create \
  --resource-group RG-Test \
  --template-file main.bicep

You check for:

Resource misconfigurations
Property errors
Dependency issues
Naming conflicts

7. Best Practices for Modifying Templates

Best Practice	Why It Matters
Use parameters for all values that may change	Avoid hardcoding
Use variables for repeated values	Easier maintenance
Use modules in Bicep for large deployments	Cleaner and reusable structure
Use latest stable API versions	Avoid outdated resources
Add comments to explain changes	Helps teams and future maintenance
Validate before deploying	Prevents failed deployments

8. Exam Tips for This AZ-104 Sub-topic

✔ You do not need to memorize every ARM syntax
✔ You must understand the structure of ARM and Bicep
✔ You should be able to identify where to edit a template
✔ Expect questions like:

“Where would you add a new parameter?”
“How do you change a resource size in a Bicep file?”
“Which part of the template defines dependencies?”
“How do you convert ARM to Bicep?”
“How do you validate a modified Bicep file?”

✔ You may see real ARM/Bicep snippets and must choose the correct modification.

Conclusion

Modifying existing ARM templates or Bicep files is a key skill for the AZ-104 exam. Focus on understanding the structure, knowing where to make changes, and validating the template before deployment. Once you understand the basic sections and syntax, modifying templates becomes straightforward and systematic.

Modify existing templates or Bicep files