Chef-client 14,15,16 aren't compatibile with Chef-server 12 due various deprecations.
This means that I need to upgrade chef-server to 13 or better on 14, on a new server, then, migrate my cookbook and repo structure.
But before i need to upgrade to chef-server 12.17.15 rIght? >> https://docs.chef.io/upgrade_server/#standalone-upgrade
What means this new licence?
Are there some specifications that I need to follow?
So bootstrap of 15 and 16 will indeed barf about the license.
The windows_package error sounds more linked to the windows cookbook as a lot of its resources have been included in core in 15.
The answer from Kallistec is 5 years old, the way Chef Client is versionned has changed since then and this affirmation doesn't stand anymore (chef-server 13 and 14 are pretty recent, chef-server 13 has come after chef-client 15 for the licensing change).
If you don't have licenses, your best bet as upgrade is latest 14 and latests chef-server 12, but this will require fixing the changes in your cookbooks.
I can't tell exactly when support for Centos8 came from memory.
No information about Chef-server 12.16.14 with client 14,15,16 for centOS8 is official supported, and/or
a lots of deprecation from chef 12.16 to 12.19 or 14 need changes in the cookbooks.
No information about chef-client 12 with chef-server 13-14 will be supported. In case I need to upgrade all clients in actual nodes.
Chef licence for 12.19 is free, 13,14 no
Packages like Nokogiri & Co. are supposed will works with chef-server 12.19 with minor upgrade, with 13,14 need to be upgraded (do need check compatibility with the deploy packets and management)
need to check Chef-Workstation