Regions and Availability Zones

Each AWS Region is a fully independent, self-contained deployment of AWS infrastructure in a specific geographic area — there are dozens of Regions worldwide (e.g. us-east-1 in Northern Virginia, eu-west-1 in Ireland, ap-south-1 in Mumbai). Regions do not share infrastructure with each other by default; data doesn't automatically replicate between Regions unless you explicitly set that up (e.g. S3 Cross-Region Replication).

Within each Region, there are typically 3 or more Availability Zones — physically separate data centers (sometimes multiple buildings), each with independent power, cooling, and physical security, but connected to the other AZs in the same Region by dedicated, redundant, low-latency fiber links (typically under 2ms round trip). This tight connection is what makes multi-AZ architectures practical: a database in AZ-a can synchronously replicate to a standby in AZ-b fast enough that it doesn't meaningfully slow down write operations.

AWS deliberately doesn't publish the exact physical locations of its data centers for security reasons, and randomizes which physical AZ maps to 'AZ-a' for different customer accounts specifically to prevent everyone concentrating their 'first AZ' choice on the same physical building.