What is the difference between Uniform and Flexible orchestration?

Uniform orchestration manages identical VM instances based on a VM profile — all VMs use the same image, size, and configuration. It is optimized for large-scale stateless workloads. Flexible orchestration lets you mix VM sizes, use individually created VMs, and spread instances across availability zones and fault domains with more granular control. Flexible mode supports features like adding existing VMs to the scale set and per-instance configuration overrides. Microsoft recommends Flexible orchestration for new deployments, and Uniform is being superseded over time.

How do autoscale rules handle flapping?

Flapping occurs when scale-out and scale-in rules trigger alternately, constantly adding and removing instances. Azure mitigates this with cooldown periods — after a scale action, the autoscaler waits for the cooldown duration before evaluating rules again. Set the scale-in cooldown longer than scale-out to allow new instances to warm up and stabilize metrics. Additionally, use different thresholds for scale-out and scale-in (e.g., scale out at 75% CPU, scale in at 40%) to create a deadband that prevents oscillation.

VM Scale Set Config Builder

ComputeAzure

Build VM Scale Set autoscaling rules, upgrade policies, and instance repair.

VM Scale Sets Configuration

Build VM Scale Set auto-scaling configs with upgrade policies, repair policies, and scheduled profiles.

Required Fields

nameresourceGroupsku.namesku.capacityautoscaleSettingsautoscaleSettings.minCountautoscaleSettings.maxCount

{
  "name": "vmss-web-prod",
  "resourceGroup": "rg-compute",
  "location": "eastus2",
  "sku": {
    "name": "Standard_D4s_v5",
    "tier": "Standard",
    "capacity": 3
  },
  "orchestrationMode": "Flexible",
  "platformFaultDomainCount": 3,
  "upgradePolicy": {
    "mode": "Rolling",
    "rollingUpgradePolicy": {
      "maxBatchInstancePercent": 20,
      "maxUnhealthyInstancePercent": 20,
      "maxUnhealthyUpgradedInstancePercent": 20,
      "pauseTimeBetweenBatches": "PT2S"
    }
  },
  "automaticRepairsPolicy": {
    "enabled": true,
    "gracePeriod": "PT30M",
    "repairAction": "Replace"
  },
  "scaleInPolicy": {
    "rules": ["OldestVM"],
    "forceDeletion": false
  },
  "autoscaleSettings": {
    "enabled": true,
    "minCount": 2,
    "maxCount": 10,
    "defaultCount": 3,
    "rules": [
      {
        "metricName": "Percentage CPU",
        "metricResourceUri": "[resourceId]",
        "timeGrain": "PT1M",
        "statistic": "Average",
        "timeWindow": "PT10M",
        "timeAggregation": "Average",
        "operator": "GreaterThan",
        "threshold": 75,
        "direction": "Increase",
        "type": "ChangeCount",
        "value": 1,
        "cooldown": "PT5M"
      },
      {
        "metricName": "Percentage CPU",
        "metricResourceUri": "[resourceId]",
        "timeGrain": "PT1M",
        "statistic": "Average",
        "timeWindow": "PT10M",
        "timeAggregation": "Average",
        "operator": "LessThan",
        "threshold": 25,
        "direction": "Decrease",
        "type": "ChangeCount",
        "value": 1,
        "cooldown": "PT5M"
      }
    ],
    "scheduledProfiles": [
      {
        "name": "weekday-peak",
        "capacity": { "minimum": 4, "maximum": 15, "default": 6 },
        "recurrence": {
          "frequency": "Week",
          "days": ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"],
          "hours": [8],
          "minutes": [0]
        }
      }
    ]
  },
  "networkProfile": {
    "subnetId": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-networking/providers/Microsoft.Network/virtualNetworks/vnet-prod/subnets/snet-web",
    "loadBalancerBackendPoolIds": ["/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/rg-networking/providers/Microsoft.Network/loadBalancers/lb-web-prod/backendAddressPools/bepool-web"]
  },
  "identity": {
    "type": "SystemAssigned"
  }
}

Generated Output

Output will appear here...

About This Tool

Azure Virtual Machine Scale Sets (VMSS) let you deploy and manage a set of identical, auto-scaling VMs behind a load balancer. Configuration involves selecting the orchestration mode (Uniform for identical instances or Flexible for mixed configurations), defining autoscale rules based on metrics like CPU or custom metrics, setting upgrade policies (automatic, rolling, or manual), and configuring instance repair policies for automatic replacement of unhealthy VMs. The VMSS Config Builder helps you define scaling rules, upgrade policies, health probes, and instance protection settings for production-grade scale sets.

When to Use This Tool

•Configuring auto-scale rules that scale out based on CPU utilization and scale in based on memory pressure with different thresholds
•Setting up rolling upgrade policies with max batch percentage, pause time, and automatic rollback on failure
•Building instance repair policies that automatically replace VMs that fail health probe checks

Frequently Asked Questions

What is the difference between Uniform and Flexible orchestration?: Uniform orchestration manages identical VM instances based on a VM profile — all VMs use the same image, size, and configuration. It is optimized for large-scale stateless workloads. Flexible orchestration lets you mix VM sizes, use individually created VMs, and spread instances across availability zones and fault domains with more granular control. Flexible mode supports features like adding existing VMs to the scale set and per-instance configuration overrides. Microsoft recommends Flexible orchestration for new deployments, and Uniform is being superseded over time.
How do autoscale rules handle flapping?: Flapping occurs when scale-out and scale-in rules trigger alternately, constantly adding and removing instances. Azure mitigates this with cooldown periods — after a scale action, the autoscaler waits for the cooldown duration before evaluating rules again. Set the scale-in cooldown longer than scale-out to allow new instances to warm up and stabilize metrics. Additionally, use different thresholds for scale-out and scale-in (e.g., scale out at 75% CPU, scale in at 40%) to create a deadband that prevents oscillation.

Related Learning Guides

Azure VM Series Guide22 min read

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