Availability Zone

Problem

You have three servers. Excellent. Unfortunately, they're all in the same data center, and that entire facility loses power. Three servers did not protect you from one shared failure.

Solution — Availability Zones

Place resources in physically separate failure domains within a region.

Region
├─ Zone A → App
├─ Zone B → App
└─ Zone C → App

Core idea: zones protect against failures affecting an entire facility or local infrastructure domain.