Always On Availability Group
Official Definition
An Availability Group (AG) provides HA/DR by hosting a set of databases that fail over together between replicas.
Simplified Explanation
Availability Groups are SQL Server’s premier high-availability solution that lets you maintain multiple synchronized copies of your databases across different servers. Unlike older solutions that worked with single databases, AGs group related databases together so they all fail over as a unit – crucial for applications that depend on multiple databases staying in sync.
The primary replica handles all the work while secondary replicas can serve read-only queries and provide automatic failover protection. You can have up to 8 replicas total, with some synchronous (guaranteed identical data) and others asynchronous (faster but slight data lag).
This flexibility makes AGs suitable for everything from local high availability to disaster recovery across continents, though they do require Windows clustering for automatic failover.
Further Reading
See the official Microsoft documentation on “Always On Availability Group” for a more detailed explanation.
