Availability Zone (AZ)

An availability zone is an isolated group of one or more data centres within a cloud region, with independent power, cooling and networking, used to run redundant copies of workloads so that one site failure does not stop a service.

An availability zone is an isolated location within a cloud region, made up of one or more data centres with independent power, cooling and networking. Zones in the same region are physically separated to limit the impact of local events such as fires or power failures, yet connected by low-latency, high-bandwidth links. AWS and Microsoft Azure use the term availability zone, while Google Cloud calls the equivalent a zone.

Deploying an application across two or more zones is the standard way to achieve high availability in the cloud. Load balancers distribute traffic across instances in several zones, managed databases can keep synchronous standby copies in another zone, and Kubernetes clusters can spread nodes and pods across zones so that the loss of one zone does not stop the service.

Zone redundancy protects against data-centre-level failures but not against a region-wide outage, a faulty deployment or data corruption, which require backups and cross-region disaster recovery. Traffic between zones may be billed and adds a small amount of latency. Provider service level agreements typically offer higher availability commitments for multi-zone deployments than for single instances.

Key points

Zones in one region are physically separate but linked by low-latency networking
Google Cloud uses the term zone for the same concept
Spreading workloads across zones is the standard pattern for cloud high availability
Zone redundancy does not replace backups or cross-region disaster recovery

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Related terms

Terms that refer to Availability Zone (AZ)

Recovery Point Objective (RPO)Cloud & AI Infrastructure