Can I add a Stand Alone instance to a Windows Failover Cluster for Always On set up?
I need to have one secondary synchronous replica with automatic failover.
I think you're asking if you need to reinstall SQL Server on the existing node you're adding to the cluster.
If it's just availability groups, and you want to add an existing instance, this is easy. You just add the computer to the cluster and enable AG in SQL Configuration Manager.
It's different to the old Failover Cluster Instances where you had to install SQL Server in "cluster mode". For a plain AG it's not required.
Just want to answer the question I asked :
To configure AOAGs with Synchronous mode + Automatic Failover -- This is possible only with Stand-Alone SQL Instances in SYNCHRONIZED state but not with SQL Server Failover Cluster Instances (Asynchronous) as the principle/point of Automatic Failover to AOAGs with FCI turns out to be a issue/conflict and not possible to enable same Automatic failover for FCI + AOAGs which is NOT possible in current versions of SQL Server 2012/2014. I learned from colleagues that this will be fixed in future version MS SQL Server 2016.