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4.1.2.3. Deploy VMs using Azure Resource Manager (ARM) Templates

💡 First Principle: ARM templates enable automated, consistent, and repeatable deployments by defining infrastructure declaratively as code, forming the foundation of Infrastructure as Code (IaC) in Azure.

Scenario: You need to deploy a full web application stack (Virtual Machines, Virtual Network, Load Balancer) to multiple environments. Each environment will have slight variations (e.g., VM size, IP ranges). You want to ensure identical deployments and prevent manual errors.

What It Is: ARM templates are the native Infrastructure as Code (IaC) mechanism in Azure for deploying resources.

Key Benefits of using ARM templates:
  • Consistency: Deploy identical environments across dev, test, and production, eliminating "configuration drift."
  • Automation: Streamline complex, multi-resource deployments without manual steps.
  • Idempotence: Running the same template multiple times yields the same result.
  • Version Control: Store templates in source control (Git) to track changes and collaborate.
Basic structure of an ARM template:
  • $schema: Specifies the template’s JSON schema.
  • contentVersion: Version of the template.
  • parameters: Input values to customize deployments.
  • variables: Values calculated from parameters or constants.
  • resources: The Azure resources to deploy.
  • outputs: Values returned after deployment.
Practical Implementation: Deploying a Template with Azure CLI
# Deploy an ARM template from a local file
az deployment group create \
  --resource-group MyResourceGroup \
  --template-file vm-template.json \
  --parameters @vm-parameters.json
Visual: ARM Template Deployment Flow
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⚠️ Common Pitfall: Hardcoding values (like VM names or sizes) directly into the template instead of using parameters. This makes the template inflexible and not reusable across different environments.

Key Trade-Offs:
  • Learning Curve vs. Power/Scalability: Writing ARM templates has a steeper learning curve than using the portal, but it is infinitely more powerful, scalable, and reliable for production environments.

Reflection Question: How do ARM templates, by enabling you to define and deploy Azure infrastructure declaratively as code, fundamentally ensure automation, consistency, and version control for VM deployments and complex environments?