Join 10.5.1 ArcGIS Servers (AGS) to a Site Created at 10.3.1

[MichaelVolz]

I have a current AGS site with AGS 10.3.1 servers on Windows 2008 virtual machines.  I am upgrading to AGS 10.5.1 on Windows 2012 virtual machines.  My current plan is to remove the existing servers from the site and then add the new servers to the site to keep the site intact.

Is this a viable path forward or do I need to create a brand new site for 10.5.1? If I need to create a new site is it because the old site holds on to the configuration settings of the 10.3.1 servers and cannot be reliably updated to 10.5.1 configuration settings?

In addition, the ArcGIS Enterprise Server documentation:

Join an existing site—Installation Guides (10.5) | ArcGIS Enterprise 

Says "A site is a deployment of ArcGIS Server. If you've installed ArcGIS Server for the purpose of adding it to an existing site, you have the opportunity to specify that site the first time you open ArcGIS Server Manager."

Is there no way to specify the site after you have opened AGS Manager for the first time?

[MichaelVolz]

Jonathan:

I see you mention Windows Server 2016 machines, so does that mean that 2016 machines are supported at 10.5.1 as I thought ESRI documentation only showed 10.5 supported up to Windows Server 2012 R2 machines?

[JonathanQuinn]

Window Server 2016 is supported at 10.5.1:

ArcGIS Server 10.5.x system requirements—Installation Guides (10.5) | ArcGIS Enterprise 

The system requirements were recently updated.