Availability Zone

An availability zone (AZ) is a physically separate location within a cloud region, made up of one or more data centers with their own power, cooling, and network. Zones in a region are close enough for low-latency connections but far enough apart that a single failure, such as a power outage or flood, does not take down more than one zone.

How It Works

A region typically contains two or more availability zones. Providers connect zones with high-bandwidth, low-latency private links. Applications achieve fault tolerance by spreading resources across zones: running compute instances in multiple AZs behind a load balancer, replicating databases across zones, and storing data redundantly. If one zone becomes unavailable, traffic and workloads shift to the remaining zones.

Zone identifiers are often randomized per account so that load spreads evenly across the provider's physical infrastructure. Multi-AZ deployment is a standard pattern for production systems and is frequently a requirement for a provider's uptime service-level agreement.

Why It Matters

Availability zones are the primary mechanism for high availability inside a single region. By isolating failure domains, they let teams survive localized outages without the cost and complexity of running across distant regions. They strike a balance: low latency for synchronous replication, with real physical separation for resilience. For stronger protection against region-wide events, teams combine multi-AZ design with multi-region strategies, which add geographic redundancy at the cost of higher latency and complexity.

Related Terms

Availability zones sit inside a region and underpin high availability, redundancy, and disaster recovery designs.