HighAvailability

High availability (HA) refers to the design, implementation, and operation of computer systems to minimize downtime and ensure continuous service delivery. The goal is to keep critical services accessible despite hardware failures, software faults, or maintenance events. Achieving HA involves reducing single points of failure, rapid detection of faults, and automatic recovery mechanisms.

Common techniques include hardware and software redundancy, replication of data, clustering, and load balancing. Redundant components such as power supplies, network paths, and storage devices help tolerate failures. Data replication across sites, synchronous or asynchronous, supports continued operation and quick data recovery. Failover clusters, database replicas, and load balancers can automatically redirect traffic when a component becomes unavailable. Health monitoring, heartbeat signals, and automated restart or failover processes help minimize downtime. In some architectures, active-active configurations run multiple instances in parallel, while active-passive setups keep standby resources ready to take over.

Architectures often involve multi-site or geo-redundant deployments to tolerate regional outages. The choice between availability, performance, and consistency depends on application requirements and often involves trade-offs described by related concepts such as RTO (recovery time objective) and RPO (recovery point objective). Service level agreements (SLAs) commonly define expected HA targets.

Organizations typically test HA through disaster recovery drills and regular maintenance, including patching, backups, and performance tuning. HA is a key consideration in IT infrastructure, cloud services, and database design, complementing security and scalability goals.