Best practices for an in-place upgrade from Server 2008r2 to 2016/2019?
Solution 1:
If you must stay with the same hardware/machines, then a two-step upgrade is your only option:
2008 to 2012, then 2012 to 2016.
But, if you have a virtual infrastructure or can use additional hardware, you can treat this as a migration rather than an upgrade.
Build new SQL servers and new IIS hosts, and then migrate the applications rather than upgrade the OSes.
Solution 2:
I'm afraid not as there is no in-place upgrade path from 2008 to 2016. At least not from Microsoft. Not sure if there're 3rd party utilities out there to achieve this.