AAG has two commit mode that we can choose: Synchronous mode, and Asynchronous mode.
While synchronous offer zero data loss, this is not intended for disaster recovery site which usually located far from data center. Asynchronous mode offer better performance, however AAG with asynchronous commit mode doesn't allow automatic failover to secondary site.
SQL Server throws error number 1480 whenever there is a change between primary and secondary roles. We can setup alert that capture those error and switch over to secondary site. Since forced failover to secondary DB can be run using this command "ALTER
AVAILABILITY GROUP [AAG Name] FORCE_FAILOVER_ALLOW_DATA_LOSS", we can use that command to switch to secondary DB using SQL alert. For more information on how to create that alert, please see reference 2.
Here's a video showing you that it can be done https://youtu.be/PhS4HhDHdFI
Reference
1. https://msdn.microsoft.com/en-us/library/hh781257.aspx
2. http://sqlmag.com/blog/alwayson-ags-and-sql-server-jobs-setting-failover-alerts
