Comment 1 for bug 1955751

It appears that Juju does the right thing in conjunction with logrotated. While Juju appears to keep file handles to the log files open, If I manually trigger a log rotation, Juju does appear to respect logrotated's signals and start logging to the new log files.

Thus, addressing this may be as simple as optionally installing the following as /etc/logrotate.d/juju:

/var/log/juju/*.log
{
    missingok
    daily
    copytruncate
    rotate 7
    notifempty
}

The above would of course be adjusted appropriately by the charm per normal operation.