Microsoft Azure Documentation

Overview of Virtual Machine Scale Sets

Azure Virtual Machine Scale Sets (VMSS) provide a way to deploy and manage a group of load-balanced virtual machines. They allow you to easily increase or decrease the number of virtual machines and the applications they host, responding to demand or scheduled patterns. This capability is crucial for building highly available and scalable applications.

Key Benefits

• High Availability: Distributes VMs across multiple fault domains and availability zones for resilience.
• Automatic Scaling: Automatically adjusts the number of VMs based on metrics like CPU usage, queue depth, or a schedule.
• Simplified Management: Deploy and manage a group of identical VMs as a single unit.
• Load Balancing: Integrates with Azure Load Balancer to distribute network traffic across VM instances.
• Application Health Monitoring: Can be configured to monitor the health of applications and replace unhealthy instances.

Core Concepts

Instance Counts and Scaling

You define a minimum and maximum number of VM instances. When demand increases, VMSS can automatically scale up to the maximum count. When demand decreases, it can scale down to the minimum count.

Orchestration Modes

VMSS offers two orchestration modes:

• Uniform Orchestration: All VM instances are identical and managed as a group. This is the traditional mode for VMSS.
• Flexible Orchestration: Allows for a mix of VM types and configurations within a single scale set, providing more control over individual VMs while still leveraging scale set features.

Upgrade Policies

Control how VM instances are updated when you change the scale set's configuration or image. Options include:

• Automatic: Updates are applied automatically to all instances.
• Manual: You must manually initiate the upgrade for each instance.
• Rolling: Instances are upgraded in batches with a configurable pause between batches.

Use Cases

• Web servers and APIs that need to handle variable traffic.
• Batch processing workloads.
• High-performance computing (HPC) applications.
• Disaster recovery scenarios.

az vmss create \
  --resource-group MyResourceGroup \
  --name myScaleSet \
  --image UbuntuLTS \
  --vm-sku Standard_D2s_v3 \
  --instance-count 3 \
  --admin-username azureuser \
  --generate-ssh-keys

Continue exploring the documentation to learn about creating, managing, and scaling your Virtual Machine Scale Sets effectively.