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Microsoft SQL Server Always On Availability Groups Architecture Design
by BF (Principal Consultant; Architecture; Engineering)

The Always On Availability Groups (AGs) feature is a high-availability and disaster-recovery solution that maximizes the availability of a set of user databases for an enterprise data estate.

Always On AGs are SQL Server’s premier HA/DR technology.

Always On AGs consist of the following main components: (Windows + SQL)

(1) Availability Group - contains user database(s).
(2) Primary replica - principal SQL Server Instance.
(3) Secondary Replica(s) - failover target SQL Server Instance.
(4) Windows Server Failover Cluster - a group of independent servers that work together to increase the availability of applications and services.
(5) Listener - unique DNS name that serves as a virtual network name (VNN).

Here is a typical architecture design for a 3-node, multi data center infrastructure.