Regions and Availability Zones
Where AWS physically lives: cities worldwide, each split into separate data centers.
A Region is a geographic area where AWS has built its infrastructure: Northern Virginia, São Paulo, Frankfurt, Tokyo and a few dozen more. Each Region is independent from the others. When you create something in AWS (a bucket in Amazon S3, a server in Amazon EC2) you pick the Region it lives in, and it stays there unless you copy it somewhere else.
Inside each Region there are several Availability Zones (AZs): groups of one or more data centers with their own power, cooling and network, far enough apart that a fire or a flood in one does not take down the others, but close enough to talk to each other in a couple of milliseconds. A Region has a code like us-east-1 and each zone adds a letter: us-east-1a, us-east-1b.
Why it matters: picking a Region near your users makes your app feel faster, and sometimes the law requires it (some data cannot leave the country). Spreading an app across two or more AZs is the standard way to survive a data center outage without anybody noticing. A bank in Buenos Aires might run its app in sa-east-1 (São Paulo) across three zones, with a backup copy in Virginia.
Keep in mind
- Regions are isolated from each other; nothing is shared or copied automatically.
- An Availability Zone is one or more data centers; every Region has at least three.
- Running in two AZs is the usual minimum for an app that must stay up.
- Prices and the list of available services differ a little from Region to Region.
