In place upgrade from Windows Server 2016 to 2022 in multi machine server site

LouEarly

Is is possible to upgrade the OS one machine at a time in a multi machine arcgis server site?  For instance, there are 3 machines each running 2016. Can we temporarily remove a machine from the site, upgrade it to 2022 then add it back to the site while the other two machines are still running 2016? We would then follow this process for the other two machines, taking down one at a time to upgrade the OS. 

ESRI recommends all machines that participate in a server site have the same OS. We are concerned that doing this will create problems.

TonyContreras_Frisco_TX

Given that your upgrade process is supported by Microsoft and you are asking about Esri's recommendation, this appears to apply for a long term configuration. There is not really much risk in having different OS's for a few hours or a couple days. As long as the ArcGIS Server version is not also being upgraded and the version of ArcGIS you have installed supports Server 2022, you should be good.

If your site can support your current load as a 2-machine site, you can remove one machine, upgrade it, re-add it and repeat the process for the remaining servers until they have all been upgraded.

The removing and (especially) adding process can sometimes be process intensive to all servers in the site, leading to the site being slow to respond or even temporarily unresponsive. You should time these operations accordingly to minimize disruption to the clients.