High availability (HA) refers to designing systems so they continue functioning even when components fail. HA architectures use redundancy, failover, load balancing, data replication, and multi-zone or multi-region deployments. The goal is to minimize downtime and ensure users can access services reliably, even during outages or maintenance.
Why it matters
Most modern applications require near-continuous uptime. HA protects revenue, user trust, and operational continuity. By eliminating single points of failure, HA systems can survive hardware failures, scaling pressure, or network disruptions.
Examples
Deploying application servers across multiple availability zones or replicating a database cluster.