While in theory automated systems such as ploy allow you to create new and up-to-date instances easily and thus in theory you would never have to upgrade existing instances because you would simply replace them with newer versions, in practice both jails and host systems will often have to be upgrade in place.
To support this, bsdploy provides a few helper tasks which are registered by default for jailhosts.
If you want to use them in your own, custom fabfile you must import them their to make them available, i.e. like so:
from bsdploy.fabutils import *
You can verify this by running the do command with -l:
# ploy do HOST -l Available commands:pkg_upgrade rsync update_flavour_pkg
You can use the pkg_upgrade task to keep the pkg and and the installed packages on the host up-to-date.
The update_flavour_pkg is useful after updating the ezjail world, so that newly created jails will have an updated version of pkg from the start. (if the pkg versions become too far apart it can happen, that new jails won’t bootstrap at all, because they already fail at installing python).
See the fabutils.py file for more details.