@JsonIgnore
    public boolean isProxyHost() {
        return isHostedVespaApplicationWithPredicate(ApplicationInstanceId::isProxyHost) &&
               Objects.equals(clusterId, ClusterId.PROXY_HOST) &&
               Objects.equals(serviceType, ServiceType.HOST_ADMIN);
    }
Is a config server (and not controller!)
application-model/src/main/java/com/yahoo/vespa/applicationmodel/ServiceCluster.java