public Set<String> hostnames() {
        return getEntries().stream()
                           .flatMap(entry -> entry.getServices().stream())
                           .map(ServiceInfo::getHostName)
                           .collect(Collectors.toUnmodifiableSet());
    }
Represents all actions to restart services in order to handle a config change.

@author geirst
configserver/src/main/java/com/yahoo/vespa/config/server/configchange/RestartActions.java