As you already know Microsoft has announced end of support for OS 2008, 2008 R2 Servers by 14th Jan 2020.
We have our two PI Servers (Versions: 2015 and 2012) running on OS 2008 R2 and planning to upgrade OS to 2012. There are multiple PI components (like PI Data Archive, PI AF, PI Analysis, PI Notification, PI Web API etc) and other custom built applications installed on one (PI version: 2015) of these Servers whereas the other Server (PI version: 2012) just contain PI Data Archive.
Can someone please suggest what could be the best approach to upgrade OS on PI Server without any risk involved. Should we go for In-Place upgrade or Parallel upgrade? if anyone has faced a similar situation before, please advise what approach did you followed.