Dellenny presents a practical guide to adopting immutable infrastructure on Azure, detailing the steps, best practices, and tooling for reliable cloud deployments with DevOps workflows.

Building Resilient Systems with Immutable Infrastructure on Azure

In modern DevOps and cloud-native architecture, immutable infrastructure is a cornerstone for building reliable, consistent, and secure systems. In this post, Dellenny explores what immutable infrastructure means, its advantages, and how to implement it effectively on Azure with industry-standard tools and workflows.

What is Immutable Infrastructure?

Immutable infrastructure is a paradigm in which servers, VMs, or containers are never updated after deployment. Instead, when a change is needed—such as a new application version or configuration tweak—a new instance is built and deployed. Old versions are destroyed, ensuring all running infrastructure matches the latest specifications.

Mutable Infrastructure:

  • Allows SSH/RDP access for manual updates
  • Prone to configuration drift
  • State is harder to reproduce

Immutable Infrastructure:

  • No in-place modifications
  • Each deployment creates new VMs or containers
  • Consistency and traceability are built in

Benefits of Immutable Infrastructure

  • Consistency: Deployments are built from controlled, versioned images/templates
  • Reliability: What’s running in production is always known and reproducible
  • Auditability: Deployments are traceable for auditing and compliance
  • Easy Rollbacks: Restoring a previous version is as simple as redeploying an older image or template
  • Security: Limiting access (e.g. no SSH/RDP) reduces the attack surface

Implementing Immutable Infrastructure in Azure

1. Define Infrastructure as Code (IaC)

Use tools like ARM templates, Bicep, or Terraform to define your infrastructure in a version-controlled way. For example:

resource myVm 'Microsoft.Compute/virtualMachines@2021-07-01' = {
  name: 'app-vm-${uniqueString(resourceGroup().id)}'
  location: resourceGroup().location
  properties: {
    hardwareProfile: {
      vmSize: 'Standard_B2s'
    }
    storageProfile: {
      imageReference: {
        publisher: 'Canonical'
        offer: 'UbuntuServer'
        sku: '18.04-LTS'
        version: 'latest'
      }
      osDisk: {
        createOption: 'FromImage'
      }
    }
    osProfile: {
      computerName: 'appvm'
      adminUsername: 'azureuser'
      adminPassword: 'SecurePassword123'
    }
    networkProfile: {
      networkInterfaces: [
        {
          id: nic.id
        }
      ]
    }
  }
}

2. Use Image-Based Deployment

Utilize Azure Image Builder, Packer, or the Azure Compute Gallery to bake application images ahead of time. Reference these images in your IaC files for reliable, repeatable deployments.

"imageReference": {
  "id": "/subscriptions/{sub-id}/resourceGroups/{rg}/providers/Microsoft.Compute/galleries/{gallery}/images/{image}/versions/{version}"
}

3. Deploy with Blue-Green or Rolling Strategies

Use Azure VM Scale Sets or App Service Deployment Slots for safe rollouts:

  • Blue-Green: Deploy a parallel environment, redirect traffic, then retire the old environment
  • Rolling Upgrade: Gradually replace old instances with new ones in controlled batches

Example configuration for rolling upgrades:

"upgradePolicy": {
  "mode": "Rolling",
  "rollingUpgradePolicy": {
    "maxBatchInstancePercent": 20,
    "maxUnhealthyInstancePercent": 20,
    "pauseTimeBetweenBatches": "PT0S"
  }
}

4. Automate Everything with CI/CD

Automate your entire workflow using Azure DevOps Pipelines, GitHub Actions, or Terraform Cloud. A typical pipeline:

  • Code Change → Build Image (e.g. Packer) → Push to Azure Compute Gallery
  • Deploy via ARM/Bicep/Terraform → Replace Instances → Validate health

Example Workflow: Web App Deployment

  1. Build App Image: Use Packer and Azure DevOps
  2. Push to Compute Gallery: Upload versioned VM images
  3. Update IaC templates: Reference new image
  4. Redeploy VM Scale Set: New instances come up, old are drained/removed
  5. Monitor Health: Use Azure Monitor / Application Insights

Resource Clean-Up Best Practices

To avoid unnecessary costs and clutter:

  • Automate resource deletion with Azure CLI or Automation
  • Set up lifecycle management policies in Azure

Azure Services for Immutable Infrastructure

  • Azure DevOps: CI/CD pipelines
  • Azure Compute Gallery: Centralized image library
  • VM Scale Sets: Automated, scalable compute pools
  • Packer: Image creation
  • Terraform / Bicep / ARM: Infrastructure as code
  • Deployment Slots: For zero-downtime app releases

Conclusion

Adopting the immutable infrastructure pattern on Azure boosts consistency, auditability, and security for cloud deployments. With Microsoft’s tooling ecosystem, the approach is mature and fully supported for enterprise workloads.

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