Azure Virtual Machine Scale Set (VMSS)

Azure Virtual Machine Scale Set (VMSS)

Azure Virtual Machine Scale Sets (VMSS) let you deploy and manage a group of identical virtual machines that automatically scale in or out based on demand. VMSS is designed for high availability, elasticity, and large-scale workloads.

In simple terms:

VMSS = multiple VMs + autoscaling + load balancing (all in one service)

Key Features of Azure VMSS

Automatic Scaling

Scale out when CPU, memory, or custom metrics increase

Scale in when demand decreases

Supports manual, scheduled, and metric-based scaling

High Availability

Distributes VMs across Availability Zones or Fault Domains

Ensures applications remain available even if a VM fails

Load Balancing (Built-in)

Integrates directly with:

Azure Load Balancer (L4)

Azure Application Gateway (L7)

Traffic is automatically distributed across VM instances

Uniform Configuration

All VMs are created from the same image and configuration

Simplifies management, updates, and patching

Cost Efficiency

Scale down when traffic is low → pay only for what you use

Works well with Spot VMs for cost savings

Common Use Cases

Web applications

Microservices

API backends

Batch processing

Dev/Test environments

Container workloads (AKS node pools use VMSS internally)

Azure VMSS vs AWS Equivalent

Azure and AWS solve the same problem but design the services differently.

Azure (Unified Approach)

Azure wraps everything into one service:

VMSS

VM provisioning

Autoscaling

Load balancer integration

Health monitoring

AWS (Modular Approach)

AWS uses multiple services together:

Azure AWS

VM Scale Set Auto Scaling Group (ASG)

VM Image Launch Template / Launch Configuration

Azure Load Balancer Elastic Load Balancer (ALB / NLB / ELB)

Integrated scaling ASG scaling policies

Conceptually the same, but:

Azure = simpler, tightly integrated

AWS = more granular and flexible