Availability Zones
AWS operates over 100 Availability Zones within several Regions around the world (current numbers can be found here: AWS Global Infrastructure). An Availability
Zone is one or more discrete data centers with independent and redundant power infrastructure,
networking, and connectivity in an AWS Region. Availability Zones in a Region are
meaningfully distant from each other, up to 60 miles (~100 km) to prevent correlated failures,
but close enough to use synchronous replication with single-digit millisecond latency. They
are designed not to be simultaneously impacted by a shared fate scenario like utility power,
water disruption, fiber isolation, earthquakes, fires, tornadoes, or floods. Common points of
failure, like generators and cooling equipment, are not shared across Availability Zones and
are designed to be supplied by independent power substations. When AWS deploys updates to
its services, deployments to Availability Zones in the same Region are separated in time to
prevent correlated failure.
All Availability Zones in a Region are interconnected with
high-bandwidth, low-latency networking, over fully redundant,
dedicated metro fiber. Each Availability Zone in a Region connects
to the internet through two transit centers where AWS peers with
multiple
tier-1
internet providers (for more information, refer to
Overview
of Amazon Web Services).
These features provide strong isolation of Availability Zones from
each other, which we refer to as Availability Zone Independence
(AZI). The logical construct of Availability Zones and their
connectivity to the internet is depicted in the following figure.