Upgrade to 2020.4.3 with Clustered SQL fails with generic Networking error : 70

During the upgrade to 2020.4.3 with clustered SQL, how to resolve when it fails with generic Networking error: -70 ?

Issue Description: Whilst upgrading to 2020.4.3, with a clustered SQL environment the following error message pops-up:

System.Exception: Error:-70, Message: Am error has occurred while installing the database. A network-related or instance-specific error occurred while establishing a connection to SQL Server.



Resolution : Modify the SQL connection string to be: “<add name=“Default” providerName=“System.Data.SqlClient” connectionString=“Data Source=IP/SQLInstanceName, port;Initial Catalog=;User ID=;” />”.
This would be the way Identity SErver is able to identify the right SQL instance and do the upgrade properly.