--- title: "Configuration of a Server Instance for Always On Availability Groups (SQL Server) | Microsoft Docs" ms.custom: "" ms.date: "06/13/2017" ms.prod: "sql-server-2014" ms.reviewer: "" ms.technology: high-availability ms.topic: conceptual helpviewer_keywords: - "Availability Groups [SQL Server], server instance" - "Availability Groups [SQL Server], about" ms.assetid: fad8db32-593e-49d5-989c-39eb8399c416 author: MashaMSFT ms.author: mathoma manager: craigg --- # Configuration of a Server Instance for Always On Availability Groups (SQL Server) This topic contains information about the requirements for configuring an instance of [!INCLUDE[ssNoVersion](../../../includes/ssnoversion-md.md)] to support [!INCLUDE[ssHADR](../../../includes/sshadr-md.md)] in [!INCLUDE[ssCurrent](../../../includes/sscurrent-md.md)]. > [!IMPORTANT] > For essential information about [!INCLUDE[ssHADR](../../../includes/sshadr-md.md)] prerequisites and restrictions for Windows Server Failover Clustering (WSFC) nodes and for instances of [!INCLUDE[ssNoVersion](../../../includes/ssnoversion-md.md)], see [Prerequisites, Restrictions, and Recommendations for AlwaysOn Availability Groups (SQL Server)](prereqs-restrictions-recommendations-always-on-availability.md). ## Terms and Definitions 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 [!INCLUDE[ssNoVersion](../../../includes/ssnoversion-md.md)] 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](../../database-mirroring/the-database-mirroring-endpoint-sql-server.md) An endpoint is a SQL Server object that enables SQL Server to communicate over the network. To participate in database mirroring and/or [!INCLUDE[ssHADR](../../../includes/sshadr-md.md)] 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 AlwaysOn Availability Groups To support [!INCLUDE[ssHADR](../../../includes/sshadr-md.md)], a server instance must reside on a node in the WSFC failover cluster that hosts the availability group, be [!INCLUDE[ssHADR](../../../includes/sshadr-md.md)] enabled, and possess a database mirroring endpoint. 1. Enable the AlwaysOn 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 AlwaysOn Availability Groups** - [Enable and Disable AlwaysOn Availability Groups (SQL Server)](enable-and-disable-always-on-availability-groups-sql-server.md) **To determine whether a database mirroring endpoint exists** - [sys.database_mirroring_endpoints (Transact-SQL)](/sql/relational-databases/system-catalog-views/sys-database-mirroring-endpoints-transact-sql) **To create a database mirroring endpoint** - [Create a Database Mirroring Endpoint for AlwaysOn Availability Groups (SQL Server PowerShell)](database-mirroring-always-on-availability-groups-powershell.md) - [Create a Database Mirroring Endpoint for Windows Authentication (Transact-SQL)](../../database-mirroring/create-a-database-mirroring-endpoint-for-windows-authentication-transact-sql.md) - [Allow a Database Mirroring Endpoint to Use Certificates for Outbound Connections (Transact-SQL)](../../database-mirroring/database-mirroring-use-certificates-for-outbound-connections.md) ## Related Content - **Blogs:** [AlwaysON - HADRON Learning Series: Worker Pool Usage for HADRON Enabled Databases](https://blogs.msdn.com/b/psssql/archive/2012/05/17/alwayson-hadron-learning-series-worker-pool-usage-for-hadron-enabled-databases.aspx) [SQL Server AlwaysOn Team Blogs: The official SQL Server AlwaysOn Team Blog](https://blogs.msdn.com/b/sqlalwayson/) [CSS SQL Server Engineers Blogs](https://blogs.msdn.com/b/psssql/) - **Videos:** [Microsoft SQL Server Code-Named "Denali" AlwaysOn Series,Part 1: Introducing the Next Generation High Availability Solution](https://channel9.msdn.com/Events/TechEd/NorthAmerica/2011/DBI302) [Microsoft SQL Server Code-Named "Denali" AlwaysOn Series,Part 2: Building a Mission-Critical High Availability Solution Using AlwaysOn](https://channel9.msdn.com/Events/TechEd/NorthAmerica/2011/DBI404) - **Whitepapers:** [Microsoft SQL Server AlwaysOn Solutions Guide for High Availability and Disaster Recovery](https://go.microsoft.com/fwlink/?LinkId=227600) [Microsoft White Papers for SQL Server 2012](https://msdn.microsoft.com/library/hh403491.aspx) [SQL Server Customer Advisory Team Whitepapers](http://sqlcat.com/) ## See Also [Overview of AlwaysOn Availability Groups (SQL Server)](overview-of-always-on-availability-groups-sql-server.md) [Prerequisites, Restrictions, and Recommendations for AlwaysOn Availability Groups (SQL Server)](prereqs-restrictions-recommendations-always-on-availability.md) [The Database Mirroring Endpoint (SQL Server)](../../database-mirroring/the-database-mirroring-endpoint-sql-server.md) [AlwaysOn Availability Groups: Interoperability (SQL Server)](always-on-availability-groups-interoperability-sql-server.md) [Failover Clustering and AlwaysOn Availability Groups (SQL Server)](failover-clustering-and-always-on-availability-groups-sql-server.md) [Windows Server Failover Clustering (WSFC) with SQL Server](../../../sql-server/failover-clusters/windows/windows-server-failover-clustering-wsfc-with-sql-server.md) [AlwaysOn Failover Cluster Instances](../../../sql-server/failover-clusters/windows/always-on-failover-cluster-instances-sql-server.md)