Technology Fundamentals
High Availability
Definition
High availability is a characteristic of a system which aims to ensure an agreed level of operational performance, usually uptime, for a higher than normal period. It is achieved by eliminating single points of failure through redundancy.
Why It Matters
For mission-critical systems like e-commerce websites or online banking, high availability is non-negotiable. It ensures the service is accessible to users at all times, preventing financial and reputational damage from downtime.
Contextual Example
Cloud providers like AWS and Google Cloud design their regions with multiple "Availability Zones" (separate data centers). By deploying an application across multiple zones, it can remain available even if one entire data center goes offline.
Common Misunderstandings
- High availability is often measured in "nines" of uptime. For example, "five nines" (99.999%) availability means the system is down for no more than 5.26 minutes per year.
- It is closely related to fault tolerance, which is the ability of a system to continue operating in the event of a component failure.