Availability Zone (AZ)

An availability zone is one of several physically isolated data centers inside a single cloud region, each with independent power, cooling, and networking, but linked to its siblings by fast, low-latency connections. Why it matters: distributing your app across two or three AZs in the same region protects you from the most common cloud failure — a single data center losing power or network — without the complexity of going fully multi-region. It's the highest-leverage reliability move most SaaS teams can make. Practical note: 'multi-AZ' is a checkbox on many managed services (databases, load balancers, Kubernetes node groups) — turn it on. Put your load balancer in front of instances spread across AZs, and enable multi-AZ replication on your primary database so a zone failure triggers an automatic failover instead of downtime. Cross-AZ traffic within a region is usually cheap or free, so there's rarely a cost reason to keep everything in one zone.