Availability is how consistently a system stays accessible and operational, while fault tolerance ensures it keeps running even if parts fail. Together, they enable resilient systems that users can rely on without interruption.

High availability is achieved by reducing single points of failure and adding redundancy. In active-active clustering, multiple nodes handle traffic at once, while in active-passive, standby nodes take over if the primary fails.

Redundancy underpins availability by duplicating components—servers, databases, or network routes—so a failure in one doesn’t halt the system. Deploying across multiple zones or regions ensures local outages don’t affect the whole application.

Failover strategies define how operations switch to backups during failures. Automatic failover detects issues and redirects traffic to healthy nodes, often aided by load balancer health checks.

Fault tolerance goes further, designing systems to detect errors and keep running. Techniques include retries with exponential backoff, circuit breakers to stop cascading failures, and distributed queues to decouple services.

Disaster recovery planning prepares for major outages, using backups, RPO/RTO objectives, and secondary databases or cloud replication to restore operations after catastrophic events.

Designing for availability and fault tolerance ensures minimal disruption during failures. These choices directly support business continuity and build user trust.