Enable the Always On availability group feature for a SQL Server instance

Applies to: SQL Server

This topic contains information about the requirements for configuring an instance of SQL Server to support Always On availability groups in SQL Server.


For essential information about Always On availability groups prerequisites and restrictions for Windows Server Failover Clustering (WSFC) nodes and for instances of SQL Server, see Prerequisites, Restrictions, and Recommendations for Always On Availability Groups (SQL Server).

Terms and Definitions

Always On Availability Groups
A high-availability and disaster-recovery solution that provides an enterprise-level replacement for database mirroring. An availability group supports a failover environment for a discrete set of user databases, known as availability databases, that fail over together.

availability replica
An instantiation of an availability group that is hosted by a specific instance of SQL Server and that maintains a local copy of each availability database that belongs to the availability group. Two types of availability replicas exist: a single primary replica and one to four secondary replicas. The server instances that host the availability replicas for a given availability group must reside on different nodes of a single Windows Server Failover Clustering (WSFC) cluster.

database mirroring endpoint
An endpoint is a SQL Server object that enables SQL Server to communicate over the network. To participate in database mirroring and/or Always On availability groups a server instance requires a special, dedicated endpoint. All mirroring and availability group connections on a server instance use the same database mirroring endpoint. This endpoint is a special-purpose endpoint used exclusively to receive these connections from other server instances.

To Configure a Server Instance to Support Always On Availability Groups

To support Always On availability groups, a server instance must reside on a node in the WSFC failover cluster that hosts the availability group, be Always On availability groups enabled, and possess a database mirroring endpoint.

  1. Enable the Always On Availability Groups feature on every server instance that is to participate in one or more availability groups. A given server instance can host only a single availability replica for a given availability group.

  2. Ensure that the server instance possesses a database mirroring endpoint.

Related Tasks

To enable Always On Availability Groups

To determine whether a database mirroring endpoint exists

To create a database mirroring endpoint

Related Content

See Also

Overview of Always On Availability Groups (SQL Server)
Prerequisites, Restrictions, and Recommendations for Always On Availability Groups (SQL Server)
The Database Mirroring Endpoint (SQL Server)
Always On Availability Groups: Interoperability (SQL Server)
Failover Clustering and Always On Availability Groups (SQL Server)
Windows Server Failover Clustering (WSFC) with SQL Server
Always On Failover Cluster Instances (SQL Server)