Comunity 3.6 to 3.9 or 3.10

[Bob]

I was using Debian 7 (CFEngine community 3.2) and upgrading to Debian 8 (CFEngine community 3.6) was relatively easy.

Now I'm trying to go to Debian 9, which uses CFEngine community 3.9 and I am overwhelmed. I am still supporting community 3.2, 3.6, and some clients have 3.9.

Reading here and the website, the best move appears to be moving to community 3.7 first. I won't claim to understand everything about moving from 3.6 to 3.7:

https://docs.cfengine.com/docs/3.7/guide-installation-and-configuration-upgrading-to-37.html

I suspect I am confused about masterfiles, which is what I thought were files I kept on the server (/etc/issue, /etc/motd, /etc/profile) that were pushed to the clients. However, the MPF seems to be related to the CFEngine version in use. In version 3.2 I had my own update.cf file, it appears this is part of the MPF now?

The "masterfiles" are stored in /var/lib/cfengine3/masterfiles on my distribution. The good news is for the 3.6 and 3.9 clients it appears to be up-to-date. The 3.2 clients have a directory, but it is empty for some reason.

Please suggest a way forward. Thanks in advance.