Comment 4 for bug 1449279

The cinder glance and nova-compute charms all use:

class CephContext(OSContextGenerator):
    """Generates context for /etc/ceph/ceph.conf templates."""
    interfaces = ['ceph']

    def __call__(self):
        if not relation_ids('ceph'):
            return {}

        log('Generating template context for ceph', level=DEBUG)
        mon_hosts = []
        auth = None
        key = None
        use_syslog = str(config('use-syslog')).lower()
        for rid in relation_ids('ceph'):
            for unit in related_units(rid):
                auth = relation_get('auth', rid=rid, unit=unit)
                key = relation_get('key', rid=rid, unit=unit)
                ceph_pub_addr = relation_get('ceph-public-address', rid=rid,
                                             unit=unit)
                unit_priv_addr = relation_get('private-address', rid=rid,
                                              unit=unit)
                ceph_addr = ceph_pub_addr or unit_priv_addr
                ceph_addr = format_ipv6_addr(ceph_addr) or ceph_addr
                mon_hosts.append(ceph_addr)