TopolearnPicking regions and zones decides your latency, resilience, data residency and even price.
A region is a set of datacenters in one geography, such as westeurope or eastus2. You choose a region for each resource; latency to users, data-residency rules, service availability and price all vary by region.
Many regions have availability zones: three or more physically separate groups of datacenters with independent power, cooling and networking, connected by low-latency links. Resources use zones in two ways:
- Zonal: pinned to one zone you pick (
--zone 1), e.g. a VM. You spread instances across zones yourself. - Zone-redundant: the platform replicates across zones for you, e.g. ZRS storage, zone-redundant SQL Database or App Service plans.
Zone numbers are mapped per subscription: zone 1 in your subscription may be a different building from zone 1 in someone else's.
Many regions also have a paired region in the same geography (West Europe with North Europe). Some services use the pair for geo-replication (GRS storage), and platform updates are rolled out to one region of a pair at a time. Newer regions may have no pair; multi-region designs can choose any secondary region.
Rule of thumb: zones protect against a datacenter failure with near-zero data loss; a second region protects against a regional outage but needs asynchronous replication and a failover plan.
Example
# Which regions does my subscription see, and which have zones?
az account list-locations \
--query "[?metadata.regionType=='Physical'].{name:name, pair:metadata.pairedRegion[0].name}" -o table
# A VM pinned to zone 2
az vm create -g rg-demo -n vm-z2 --image Ubuntu2404 --zone 2 \
--admin-username azureuser --generate-ssh-keysRemember
- Region = where it runs; zone = which independent datacenter group inside the region
- Zonal resources are pinned; zone-redundant ones are replicated for you
- Zones guard against a datacenter failure, regions against a regional outage
Watch out for
- Deploying three VMs "for high availability" all in the same zone (or with no zone at all).