We started getting Alerts:
Could not connect because the maximum number of '1' dedicated administrator connections already exists. Before a new connection can be made, the existing dedicated administrator connection must be dropped, either by logging off or ending the process. [CLIENT: 127.0.0.1]
It's seemed a classical alert when port scanning is taking place but our infrastructure confirmed that no jobs/port scanning configured to run at those times, nor any other tasks.
With a help of SQL job and holding table, found out that it's the SQL Server Service Account that tries to connect, approx every 4 hours e.g. 12:00 16:00 and so on, with a program name: Net SqlClient Data Provider. I've added the host_process_id column, identified the PID, but there were no processes with the same PID in the windows task manager. Oddly enough, there are no entries in the log: "Dedicated admin connection support was established", just the following ones:
16:00:05 Could not connect because the maximum number of '1' dedicated administrator connections already exists. Before a new connection can be made, the existing dedicated administrator connection must be dropped, either by logging off or ending the process. [CLIENT: 127.0.0.1]
16:00:11 Dedicated administrator connection has been disconnected. This is an informational message only. No user action is required.
No clues in Windows Event Viewer logs or Windows Cluster logs. This is only happening on an active node of AlwaysOn Availability Group.
Ladies and gentlemen, how can we troubleshoot the issue further?