@Override
    public Set<HostInfo> getHosts() {
        return hostSystem().getHosts().stream()
                           .map(HostResource::getHostInfo)
                           .collect(Collectors.toCollection(LinkedHashSet::new));
    }
Return a collection of all hostnames used in this application
config-model/src/main/java/com/yahoo/vespa/model/VespaModel.java