Redundancy is the deliberate duplication of components, data, or pathways in a system so that the failure of any single element does not cause overall failure. It is a foundational technique for fault tolerance, implemented through replicas, standby nodes, mirrored storage, and multiple network routes. By eliminating single points of failure, redundancy raises availability at the cost of additional resources.
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- Patterns range from active-active and active-passive replication to N+1 hardware provisioning and geographic distribution across availability zones. Designers balance the cost of extra capacity against the target availability, often combining redundancy with health checks and automatic failover.