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configure-virtual-machine-availability

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tagsaz-104, compute, module, availability, vmss, scaling

2 min read

Module 2 — Configure virtual machine availability

Grounded in MS Learn: az-104-manage-compute-resources → Configure virtual machine availability (learn.wwl.configure-virtual-machine-availability)

Overview

Second module of the AZ-104 compute path. Configure high availability and scaling for VMs: availability sets, availability zones, fault/update domains, Virtual Machine Scale Sets, and autoscaling.

Learning objectives (authoritative)

  1. Implement availability sets and availability zones.
  2. Implement update and fault domains.
  3. Implement Azure Virtual Machine Scale Sets.
  4. Autoscale virtual machines.

Concepts introduced

  • Availability set — fault domains (FDs) + update domains (UDs) within a region; ≥2 VMs for SLA.
  • Availability zones — physically isolated datacenters in a region for zone-level failure tolerance.
  • Fault domain vs update domain semantics (rack/power isolation vs sequential maintenance reboots).
  • Virtual Machine Scale Sets (VMSS) — identical VM fleets with horizontal scale + automatic FD/zone spreading.
  • Autoscaling — vertical (size) vs horizontal (scale out/in) scaling rules on min/max instances.

Key terms & commands

  • Availability: az vm create --zone 1 (zonal) vs availability-set via az vmss/az vm availability-set.
  • Scale sets: az vmss create --instance-count 5 --autoscale-min 3 --autoscale-max 10
  • Autoscale rules: az monitor autoscale create --resource <vmss> --min 3 --max 10 --count 5 (CPU% / metric / schedule based).
  • “Vertical” = resize VM size (deallocate → az vm resize); “Horizontal” = add/remove instances in a scale set.

Hands-on

  • Create a 2-VM availability set and confirm FD/UD assignment → shows rack-level protection.
  • Build a VMSS with autoscale on CPU%, trigger load and watch instances scale out>in.
  • Compare a zonal VM deployment (choose zone) with a regional one.

Exam focus

  • Availability set vs availability zones — mutually exclusive for one VM/scale set; when each applies.
  • Fault domain (hardware share) vs update domain (maintenance group) — classic questions.
  • Horizontal scaling = scale sets; vertical scaling = resize a VM/instance.
  • Autoscale requires setting min/max and a default count; rules can be metric- or schedule-based.
  • 2+ VMs in a set → availability SLA; zones → higher/99.99% resilience where supported.

Path MOC · availability-set · availability-zones · virtual-machine-scale-set · azure-vm · Prev: VMs

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