What is the recommended process of upgrading Availability Groups with one Sync Replica from SQL 2014 to 2016?
My understanding is that in-place upgrades are not really liked among database professionals. Is there a way to avoid in-place upgrades in Availability Groups? Is there a possibility to join a 2016 server into an existing 2014 availability group and to failover there, then "kill" one of the other instances and upgrade it? (e.g. by removing/re-installing SQL side-by-side on the same host)
Are there any other upgrade scenarios that we should consider?
The ideal solution would be that we always have 2 online replicas, and that we don't need to do any in-place upgrades.
Best Answer
The short answer is yes, much the same as when you mirror from a lower version to a higher version. Make sure you do not have the 2016 as readable so it's not trying to upgrade the database version. That said I haven't tried this, just going on how log shipping/mirroring work.
If it works it is only supported doing this as a means to upgrade, leaving 2014 replicating to a 2016 replica for extended periods of time is not going to be supported by MSFT if you hit an issue.