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H

High Availability

High availability designs systems to remain operational with minimal downtime through redundancy and failover.

What is High Availability?

High availability (HA) refers to systems designed to be operational for a high percentage of time, typically 99.9% or higher, through redundancy and automatic failover mechanisms.

HA patterns

Active-passive, Active-active, N+1 redundancy, Geographic distribution.

Common misconceptions

  • "HA prevents all outages" — Minimizes, doesn't eliminate
  • "More 9s is always better" — Cost increases exponentially
  • "Cloud means automatic HA" — Must be architected