Azure-in-bullet-points

VM Scale Sets (VMSS)

• Group that holds identically configured VM’s
• Used for
  • Need to create and manage multiple VMs
    • Centrally create and manage multple VMs (Windows Server or Linux)
  • Need for high availability and app resiliency
    • Horizontal scaling, scaling up and down based on spikes
  • Need for large (1000) scale
    • E.g. Azure Batch uses scale sets under the hood
  • Need for IaaS autoscale
    • Scale out and in based on metrics based autoscale

PaaS Scaling vs IaaS Scaling

• Azure App Service
  • High agility at the expense of administrative power
  • The underlying Hyper-V Vms are almost totally abstracted from you
  • Easy manual, scheduled, or automatic scale out and scale back
• Virtual Machine Scale Set (VMSS)
  • Maximum administrative power at the expense of agility
  • VMSS represents Azure’s approach to IaaS horizontal scaling

Deploying a VM Scale Set

• Create virtual machine scale set
  • Availability zone
    • Scale scale sets across one and more availability zones
    • ❗ All regions do not support availability zone
  • Instance count & instance set
  • Low priority
    • Take advantage of unutilized capacity
      • Compute power that customers/Microsoft is not using
      • Save costs
    • Good for workloads that can handle interruption
      • Stateless workloads
      • VMs in the scale set may be evicted at any time
      • You set eviction policy:
        • Stop / Deallocate
        • Delete
  • Use manage/unmanaged disks
    • ❗ Managed disks are not supported with availability zones
  • Networking
    • Application Gateway
      • 💡 Useful if your scale sets are web servers
      • ❗ Do not support RDP
    • Load Balancer
      • Supports RDP
      • You set public IP address name and domain name label (domain-name.region.cloudapp.azure.com)
• You can also use ARM template e.g. Deploy a Windows VM Scale Set with a Custom Script Extension that deploys VM’s, load balancer and a powershell script to be executed after deployment.

Connecting to VMs

• In Settings -> Instances you can see all the instances
• To connect to individual instances you need load balancer and NAT (network address translation)
  • You can’t RDP/SSH into individual instances directly
  • You can connect to load balancer IP’s (see in Load Balancer -> Inbound NAT rules)
  • NAT maps different VM’s on different ports.

Configuring Autoscale

• Manual: Through Portal/SDK/CLI/PowerShell
• Autoscale
• Scheduled: If you know when the load will be high you can plan for that and scale with time triggers
• Metrics: Use various metrics from various sources to determine when to scale in/out
• Manage in VMSS -> Scaling ->
  • Enable auto-scaling
  • Select scale-mode
  • Scale based on metric
    • Add rule
    • E.g. increase instance count by 1 when CPU procentage above 70%
    • 💡 You should also create scale mode that bringd down the scale count
    • Properties
      • Duration: Good to not be confused when scaling out/in, so set a duration to e.g. 10 minutes
      • Cooldown: Waits after scale operation before new scale operation
  • Scale to specific instance count
    • Time-based scaling
    • Set start and end date

This site is open source. Improve this page.