SQL Server Distributed Availability Group Usage Pattern I have got a client with DAG setup on 2016 &amp; 2017 servers. I understand that their usage is most likely for DR purposes. What I'm a little unclear on (and I can't find any info on it) is how they are connected to (if at all). With a DAG / AG setup, does the application layer still only connect to the underlying AG (and not the DAG itself)? I've tried to connect to the DAG via SSMS and cannot. Is this by design? Does anything actually connect to the DAG itself or is it just in place to manage the synchronization across AGs? Any info most appreciated guys (and girls) :)

Regards,

Glenn
The documentation for Distributed availability groups states:


  Although each underlying availability group of the distributed availability group has a listener, a distributed availability group has no listener.


So there is no way for a client to connect to a distributed AG because there is no listener for it.  Clients must connect to the listener of the AG that is currently the primary.

In order to fail over a DAG and provide connectivity for clients, you would need to initiate failover on the DAG, and then create a listener on the DR cluster with the same name as the current listener that clients connect to.

If you are using Enterprise edition, creating a DR node in the cluster and making it an asynchronous replica in the regular availability group is usually a better option, so if you haven't considered that I recommend looking into it.