TL;DR

High availability (HA) is a system’s ability to keep serving users when individual components fail, from a single server up to a whole cloud region or provider. It is measured in nines: 99.9% allows about 8 hours 46 minutes of downtime a year, 99.99% about 52 minutes, and 99.999% about 5 minutes 15 seconds. HA works by removing single points of failure through redundancy, health checks, automatic failover, and replicated data. Most teams need fewer nines than they think, and the jump from four nines to five is mostly an architecture decision: it takes locations that do not fail together. Platforms such as Control Plane package that architecture, with a 99.999% availability SLA for workloads running at least two replicas in at least two locations.

What is high availability?

High availability means a system is designed to stay operational for a very high percentage of the time. Hardware breaks, deployments go wrong, and networks and cloud regions fail.…