@when_not('apt.installed.lets-encrypt')
def check_version_and_install():
    series = lsb_release()['DISTRIB_CODENAME']
    if not series >= 'xenial':
        log('letsencrypt not supported on series >= %s' % (series))
        return
    else:
        charms.apt.queue_install(['lets-encrypt'])
        charms.apt.install_queued()