High availability (HA) is an architectural approach that reduces service interruption by removing single points of failure and using redundancy, health checks and failover. It can apply to power, networks, compute, storage, applications and people, but duplicating one component does not make the whole service highly available. Availability percentages require a defined measurement window, exclusions and service boundary; “five nines” is a target, not a feature. HA is also different from backup and disaster recovery: replicated corruption or a regional dependency can affect redundant nodes at once. Design should examine quorum, capacity during failure, maintenance, data consistency and failback. Regular fault tests and observed recovery times are needed to confirm that automation works and that dependent services remain usable.
IT glossary
High availability (HA)
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