private Set<ServiceInstance> servicesDownAndNotInGroup() {
        if (servicesDownAndNotInGroup == null) {
            servicesDownAndNotInGroup = servicesNotInGroup.stream().filter(this::serviceEffectivelyDown).collect(Collectors.toSet());
        }
        return servicesDownAndNotInGroup;
    }
A description of the hosts outside the group that are allowed to be down,
and a description of the services outside the group and outside of the allowed services
that are down.
orchestrator/src/main/java/com/yahoo/vespa/orchestrator/model/ClusterApiImpl.java