private Layer identifyInstanceLayer(String layer) {
        if (StringUtil.isEmpty(layer)) {
            return Layer.GENERAL;
        } else {
            return Layer.nameOf(layer);
        }
    }
Identify the layer of instance. Such as ${@link Layer#FAAS}.
oap-server/server-receiver-plugin/skywalking-management-receiver-plugin/src/main/java/org/apache/skywalking/oap/server/receiver/register/provider/handler/v8/ManagementServiceHandler.java