private static Collection<ServiceCluster> filter(Set<ServiceCluster> controllerClusters,
                                                            ClusterId contentClusterId) {
        ClusterId clusterControllerClusterId = new ClusterId(contentClusterId.s() + "-controllers");

        return controllerClusters.stream().
                filter(cluster -> cluster.clusterId().equals(clusterControllerClusterId)).
                toList();
    }
@return The set of all Cluster Controller service instances for the application.
orchestrator/src/main/java/com/yahoo/vespa/orchestrator/model/VespaModelUtil.java