What is high availability in the cloud?
High availability means designing a system so it stays up and running even when parts of it fail. Instead of one server that becomes a single point of failure, you run multiple copies across different zones, with a load balancer sending traffic to the healthy ones. The goal is little to no downtime, even during failures.
How you achieve it
- Redundancy: run more than one copy of each component.
- Multiple zones: spread copies across availability zones.
- Load balancing: route traffic away from failed servers.
- No single point of failure: avoid any one part that can take everything down.
If one server or even a whole data centre goes down, requests are simply served by the others. Users may not even notice, which is the point of high availability.
The phrase to use is avoid a single point of failure. Explaining that you remove any one component whose failure would break the whole system is the heart of a good high availability answer.
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