I have done all upgrades from 2.12 over 2.13, 2.14, 2.15, 2.16 to 2.18 ( I skipped 2.17)
The only thing to really watch out for in my opinion with regards to the pure upgrade path is the SQL database compatibility.
Once you are sure that all components are compatible with the new release of App Volumes, the upgrade does not take that long.
- I usually block new logons during the upgrade, VDIs with attached AppStacks/writeables should not be impacted.
- If you have more then one App Volumes instance, do one at a time, do not upgrade simultaneously
- I also usually look at differences in the logoff.bat, prestartup.bet, shell start.bat, ... between the old and the new versions of appvolumes and upload the new or adapted once to the writeable volumes. I have adapted these files and have now a set of script files that work better for the several clients I work for (see App Volumes writeable: logoff.bat, prestartup.bat, shellstart.bat, shutdown.bat, snapvol.cfg and startup.bat files)
- I am not yet upgarding to version 4.0 as I have seen and heard of too many problems with 4.0. For the moment I am sticking with 2.18
This operational tutorial on Tech Zone covers upgrade considerations, including the options for a full change window or rolling upgrade: