private Set<HostSpec> contentHostsOf(VespaModel model) {
        return model.allocatedHosts().getHosts().stream()
                    .filter(spec -> spec.membership()
                                        .map(membership -> membership.cluster().type().isContent())
                                        .orElse(false))
                    .collect(toUnmodifiableSet());
    }
Returns a restart action for each container that has turned on {@link QrConfig#restartOnDeploy()}.

@author bjorncs
config-model/src/main/java/com/yahoo/vespa/model/application/validation/change/ContainerRestartValidator.java