High Availability
Designing systems to stay operational with minimal downtime, even when components fail.
High availability (HA) means designing a system to keep operating when individual components fail, usually expressed as a percentage uptime target in a Service Level Agreement. Azure delivers HA through redundancy: Availability Zones are physically separate datacenters within a region, while Availability Sets spread virtual machines across fault domains and update domains within a single datacenter. A common exam trap is confusing HA with disaster recovery: HA keeps a workload running during routine failures in the same region, whereas disaster recovery handles full-region outages by failing over to a second region. Azure Load Balancer and Traffic Manager route traffic away from unhealthy instances.
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