def get_nagios_unit_name(relation_name='nrpe-external-master'):
    """
    Return the nagios unit name prepended with host_context if needed

    :param str relation_name: Name of relation nrpe sub joined to
    """
    host_context = get_nagios_hostcontext(relation_name)
    if host_context:
        unit = "%s:%s" % (host_context, local_unit())
    else:
        unit = local_unit()
    return unit