The glance-simplestreams-sync charm places an entry into /etc/cron.daily which is a symlink to /usr/share/glance-simplestreams-sync/glance-simplestreams-sync.py, but the filename is glance-simplestreams-sync.py.
As per the cron manpage this will never run:
Files in this directory have to be owned by root, do not need to be executable (they are configuration files,
just like /etc/crontab) and must conform to the same naming convention as used by run-parts(8): they must con‐
sist solely of upper- and lower-case letters, digits, underscores, and hyphens. **This means that they cannot
contain any dots.**
Emphasis added by me to point out the relevant part.
Simply renaming the cronjob to /etc/cron.daily/glance-simplestreams-sync should fix this issue.
This bug combined with LP#1356472 can make juju unbootable on an Openstack cloud using this charm.
Please let us know if you have any questions about this.
"""
filename requirements of run-parts: they must be entirely made up of
letters, digits and can only contain the special signs underscores
('_') and hyphens ('-'). Any file that does not conform to these
requirements will not be executed by run-parts. For example, any file
containing dots will be ignored. This is done to prevent cron from
running any of the files that are left by the Debian package management
system when handling files in /etc/cron.d/ as configuration files (i.e.
files ending in .dpkg-dist, .dpkg-orig, and .dpkg-new).
"""