Joey D’Antoni shares some thoughts on distributed Availability Groups in SQL Server 2016 and later:
I’m writing this post because I’ve been mired in configuring a bunch of distributed availability groups for a client, and while the feature is technically solid, the lack of tooling can make it a challenge to implement. Specifically, I’m implementing these distributed AGs (please don’t use the term DAG as you’ll piss off Allan Hirt, but more importantly its used in Microsoft Exchange High Availability, so it’s taken) in Azure which adds a couple of additional changes because of the need for load balancers. You should note this feature is Enterprise Edition only, and is only available starting with SQL Server 2016.
Read on for some of the positives around distributed AGs, as well as some negatives (mostly around the lack of tooling).