Availability zones
What it is
Availability zones are physically separate datacenters within an Azure region — each zone has independent power, cooling, and networking. By placing VMs (or a scale set) in multiple zones, you survive a whole-zone failure. Zonal isolation is the strongest availability option within a region.
Why it exists
Fault/update domains protect against rack-level loss; a zone failure (entire datacenter in a region) is a bigger blast radius. Zones give you 99.99% availability and true regional-disaster tolerance inside one region for the workloads that can afford the cost.
Key ideas
- Usually a region has 3 zones. Resources are tagged zone 1/2/3 or use zone-redundant placement.
- Zone-redundant services (LB, storage, App Service plans) replicate automatically across zones.
- For VMs: distribute replicas across the zones via zonal deployment or a zone-redundant scale set.
- Zone-redundant storage (ZRS) and zone-redundant managed disks keep data available when a zone fails.
- Zones are available in select regions only — not every Azure region exposes zones (exam checks this).
How it fits (diagram)
Diagrams courtesy of Microsoft Learn / Azure docs: availability-zones/az-overview
Exam notes
- Zones ⊄ availability sets: you choose either the wider failover (zones) or the rack-level spread (set), per VM/scale set — not both for the same deployment.
- Zone-redundant options exist for Azure Load Balancer (Standard), App Service plans, and storage — AZ-104 asks which services are zone-redundant.
- Only launch into zones if the region supports them; check
Get-AzLocation/ docs. - Zonal vs regional: AZ-104 wants you to pick zones when you need datacenter-level redundancy.
Related
Path MOC · azure-vm · availability-set · virtual-machine-scale-set · managed-disks
📘 Source: Microsoft Learn — Availability Zones