Availability
Definition
Availability ensures that authorized users can reliably access systems, applications, and data when needed, even during failures, surges, or adverse events.
Examples
- An online banking platform runs across multiple data centers so that if one site fails, customers can still log in and transact.
- A hospital’s electronic health record system uses failover databases and tested backups so clinicians can access charts during an outage.
Overview
Availability is the third pillar of the CIA Triad and focuses on keeping services and information usable when needed. A system with perfect confidentiality and integrity is still ineffective if legitimate users cannot access it. Availability blends engineering resilience, capacity planning, operational excellence, and defensive controls so that routine faults, traffic spikes, maintenance activities, or attacks do not interrupt critical business functions. Well-designed availability treats failure as normal: components can break without taking down the service.
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