private String entityDescription(String entity, boolean plural) {
        String pluralSuffix = plural ? "s" : "";
        return isConfigServer() ? "config server" + pluralSuffix :
               isConfigServerHost() ? "config server host" + pluralSuffix :
               isController() ? "controller" + pluralSuffix :
               isControllerHost() ? "controller host" + pluralSuffix :
               isProxy() ? (plural ? "proxies" : "proxy") :
               isProxyHost() ? "proxy host" + pluralSuffix :
               isTenantHost() ? "tenant host" + pluralSuffix :
               entity + pluralSuffix + " of {" + serviceType + "," + clusterId + "}";
    }
Is a config server (and not controller!)
application-model/src/main/java/com/yahoo/vespa/applicationmodel/ServiceCluster.java