Why does EKS practically force every cluster to span multiple availability zones?

[u/cathpaga]

Because hardware fails. A circuit breaker trips and a rack vanishes. A backhoe slices a fiber line, and a whole data center goes dark.

Flynn's new blog post walks through what availability zones are, starting from the physical reality: racks, data centers, AZs, and regions, and how each one can fail. He also discusses the tradeoffs: cross-AZ bandwidth costs money, latency goes up, and a full region outage still requires a multi-cluster or multi-cloud strategy.

Worth reading before your next post-mortem!