AZs

AZs, or Availability Zones, are a cloud infrastructure concept used to improve fault tolerance and resilience within a geographic region. A region typically comprises multiple AZs, each representing a physically separate data center or group of data centers with its own independent power, cooling, and networking. The AZs in a region are connected by high-speed networks to enable inter-zone communication with low latency while ensuring that failures in one zone do not automatically affect others. This separation reduces shared risks such as power or cooling outages.

Resources can be distributed across AZs to achieve higher availability. Common patterns include running application servers in multiple AZs behind a load balancer and configuring databases with cross-AZ replication or standby replicas. In a typical setup, if one AZ becomes unavailable, services can fail over to resources in another AZ with minimal disruption. Regions with AZs provide disaster recovery options and help meet uptime objectives.

Notes on use and scope: the general concept is similar across major cloud providers, though naming and specifics vary. Availability Zones are a central feature in many clouds, including AWS and Azure, while some providers use the term zones or regions with multiple zones. Proper use of AZs involves considerations such as cross-zone data transfer costs, inter-zone latency, and the desired consistency and failure-handling guarantees. While AZs improve resilience, they do not eliminate all failure modes, and applications should be designed to tolerate cross-AZ replication and maintenance events.