Updating windows 2016 to sp4
Downtime after the initial failover will depend on the number of databases in the Availability Group.
If you plan on failing back to the original primary, this step will not be repeated when you fail back.
var microsoft = microsoft
The other option for upgrading SQL Server 2016 and later is through the use of a distributed availability group.Suppose you are running three AGs on three server nodes with all replicas in synchronous commit mode as shown in the following table: To perform a rolling upgrade of a distributed availability group, first upgrade all of the secondary replicas.Next, failover the forwarder, and upgrade the last remaining instance of the second availability group.Warning Installing a new instance or new version of SQL Server to a server that has an older version of SQL Server installed may inadvertently cause an outage for any availability group that is hosted by the older version of SQL Server.This is because during the installation of the instance or version of SQL Server, the SQL Server high availability module (RHS. This results in a temporary interruption of your existing availability groups in the primary role on the server.