Alternatehost

Alternatehost is a concept in information technology referring to a backup or standby host that can assume operations if the primary host becomes unavailable. It is used to improve service availability, continuity, and disaster resilience across networks, applications, and data services. An alternatehost typically runs the same services as the primary and maintains a synchronized state or up-to-date data to minimize disruption during failover.

Implementation approaches vary and are often tailored to organizational needs. Common methods include DNS-based failover, where queries are redirected to the alternatehost after a failure is detected; virtual IPs or floating IPs that can be reassigned to the alternate host; and load balancers that route traffic away from the failed node. Clustering or replication strategies may be employed to keep the alternatehost in sync, using mechanisms such as synchronous or asynchronous data replication, heartbeats, and state transfer. Automated health checks and fencing controls are used to prevent split-brain situations and ensure a clean handoff.

Use cases for alternatehosts include web servers, application servers, database replicas, file services, and VPN gateways. Key considerations involve recovery time objective (RTO), recovery point objective (RPO), data consistency, failover detection latency, and the potential impact of DNS caching or session state during switchovers. The design choice between active-passive and active-active configurations affects complexity, cost, and performance.

See also: high availability, failover, load balancing, clustering, disaster recovery, data replication, virtual IP.