High Availability (HA) refers to systems designed to remain operational and accessible for extended periods, typically measured as uptime percentages (99.9%, 99.99%, etc.). HA is crucial because:
The goal is to eliminate single points of failure through redundancy, failover mechanisms, and robust system design. For example, 99.9% availability means approximately 8.77 hours of downtime per year, while 99.99% allows only 52.6 minutes annually.
