Prerequisites for Installing AlwaysON Availability Groups

With SQL Server 2012 Microsoft introduced the AlwaysOn Availability Group feature, and since then many changes and improvements have been made. Will cover the prerequisites and steps for installing AlwaysON in your SQL Server 2019 environment.

1. Prerequisites
2. Add Windows Failover Cluster (WSFC)
3. Install AlwaysOn

Prerequisites

Before implementing your AlwaysOn Availability Group (AG), make sure you have everything in your environment ready to go.  There are several prerequisites that need to be addressed to ensure a successful deployment.  

Windows

• Do not install AlwaysOn on a domain controller
• Operating system must be Windows 2012 or later
• Install all available windows hotfixes on every server (replica)
• Windows Server Failover Cluster (WSFC) must be installed on every replica
• .Net 3.5.1 or greater must be installed on every replica

SQL Server

• Each server (replica) must be a node in the WSFC
• No replica can run Active Directory services
• Each replica must run on comparable hardware that can handle identical workloads
• Each instance must run the same version of SQL Server, and have the same SQL Server collation
• The account that runs SQL Services should be a domain account

Network

• It is recommended to use the same network links for communication between WSFC nodes and AlwaysOn replicas

Databases

Databases in an AlwaysOn group must be:

• user database (no system databases)
• read/write
• multi-user
• do not use AUTO_CLOSE
• full recovery mode
• not be configured for database mirroring

For a complete and detailed explanation of prerequisites, go here:  https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/prereqs-restrictions-recommendations-always-on-availability?view=sql-server-ver15