Janitor
Topology
A Janitor instance will be started on every host that does not match the
scheduling rule (default is janitor.exclude=true).
Operation
This will run a task daily (by default) that will delete any unused image, and any orphaned volume. The rancher container images are excluded from the list of images to clean up, and you can add your own containers to the exclude list if you wish.
This will halp to prevent the /var/lib/docker filesystem from filling up with old and unused container images.