CLZ-260 - Windows VMSS Manual Scaling

Service or workflow illustration. The lesson defines the exact resource settings. Open at full size.

Goal

Deploy a reusable Windows IIS Virtual Machine Scale Set behind Standard Load Balancer and change capacity intentionally through a validated integer input.

Arrows show the learning sequence, not service traffic. Azure deployment. Open at full size.

Prerequisites

• Complete CLZ-250.
• Quota for the chosen vm_size multiplied by instance_count.
• Understand that scale-set instances are replaceable members, not individually named servers.

Architecture

Lesson-specific teaching diagram. Read the arrow legend and the accompanying architecture explanation. Azure deployment. On narrow screens, scroll the diagram horizontally. Open at full size.

The lesson supplies a web subnet and generated administrator credential to the shared windows-iis-vmss module. The module creates a uniform Windows VMSS, IIS bootstrap, Standard Load Balancer, health probe, HTTP rule, and explicit outbound rule.

Resources And Cost

Relative cost: High. VMSS instance count and size dominate; the Standard public IP and managed OS disks also incur charges.

Component	Purpose and principal cost driver
Windows VMSS	Uniform IIS instances; capacity is changed manually.
Shared VMSS module	Encapsulates load balancer, explicit outbound rule, public IP, bootstrap, and outputs.
VNet and web NSG	Allows the public HTTP teaching path to healthy instances.

Inputs

Input	Required substitution or decision
subscription_id	Required for Azure plan, apply, and destroy; use the exact subscription GUID.
environment	Keep dev for the lab unless testing another environment boundary.
location	Select a supported region with sufficient quota.
name_prefix	Use a short lowercase prefix.
admin_username	Nonreserved administrator name used by the scale set.
vm_size	Small Windows size applied uniformly to all instances.
instance_count	Positive whole number; keep it small because it directly multiplies cost.

Keep real subscription IDs, CIDRs, domains, endpoint names, and secrets in untracked local files or environment variables.

Deploy

Review the plan and lesson-specific gates before deliberate execution. Local-only and read-only lessons create no Azure resources. Open at full size.

Run from the repository root in PowerShell 7:

Set-Location CLZ-260-windows-vmss-manual-scaling
if (-not (Test-Path terraform.tfvars)) {
  Copy-Item terraform.tfvars.example terraform.tfvars
}
$subscriptionId = az account show --query id --output tsv
terraform init -lockfile=readonly
terraform fmt -check
terraform validate
terraform plan -var "subscription_id=$subscriptionId" -out tfplan
terraform show tfplan
terraform apply tfplan

Validate

The shared VMSS module uses a Manual upgrade policy. An IIS extension added to the model may require explicitly updating existing instances. Review the instance model and extension status before expecting healthy HTTP responses:

$resourceGroup = terraform output -raw resource_group_name
$scaleSetName = az vmss list --resource-group $resourceGroup --query '[0].name' --output tsv
az vmss list-instances --resource-group $resourceGroup --name $scaleSetName --expand instanceView --output json
# Deliberate Azure change: update these lab instances to the latest model after review.
az vmss update-instances --resource-group $resourceGroup --name $scaleSetName --instance-ids '*'

Follow Microsoft's VMSS application deployment guidance. Wait for successful extension execution and probe health before checking HTTP.

$resourceGroup = terraform output -raw resource_group_name
$url = terraform output -raw vmss_load_balancer_url
(Invoke-WebRequest -Uri $url -UseBasicParsing).StatusCode
az vmss list --resource-group $resourceGroup --query '[].{name:name,capacity:sku.capacity,size:sku.name,state:provisioningState}' --output table
$lb = az network lb list --resource-group $resourceGroup --query '[0].name' -o tsv
az network lb outbound-rule list --resource-group $resourceGroup --lb-name $lb --output table

Expected result:

• HTTP returns 200 after the probe marks instances healthy.
• VMSS capacity equals the requested integer and its size equals vm_size.
• The module-created Load Balancer has an explicit outbound rule.

Troubleshooting

Gather evidence, repair the cause, and rerun verification. Open at full size.

Symptom	Resolution
HTTP is unavailable immediately after apply	Wait for model deployment, extension execution, and probe health.
A fractional count fails	Use a positive integer; the module validates instance cardinality.
Scale-out fails on quota	Reduce capacity/size or choose a region with verified quota before retrying.

Cleanup

Use the lesson state and cleanup instructions. Preserve remote-state dependencies until consumers are removed. Open at full size.

$resourceGroup = terraform output -raw resource_group_name
terraform destroy -var "subscription_id=$subscriptionId"
az group exists --name $resourceGroup

The VMSS instances, Load Balancer, public IP, and network are deleted.

Production Delta

• Build and patch a versioned image, use rolling upgrade policy and application health, and collect guest diagnostics.
• Use autoscaling with tested bounds where demand changes; govern egress with NAT Gateway or Firewall when appropriate.

Exercises

1. Increase capacity by one, review the plan, apply, and prove the new instance count.
2. Change only vm_size in a disposable plan and inspect the scale-set model update.

Navigation

← CLZ-250 - For Each with Windows VMs | Curriculum | CLZ-270 - Windows VMSS Autoscaling →