private void addInclude(Element parentElement, Element include) {
        String dirName = include.getAttribute(IncludeDirs.DIR);
        app.validateIncludeDir(dirName);

        List<Element> includedFiles = Xml.allElemsFromPath(app, dirName);
        for (Element includedFile : includedFiles) {
            List<Element> includedSubElements = XML.getChildren(includedFile);
            for (Element includedSubElement : includedSubElements) {
                Node copiedNode = parentElement.getOwnerDocument().importNode(includedSubElement, true);
                parentElement.appendChild(copiedNode);
            }
        }
    }
Allocate a container cluster without a nodes tag
config-model/src/main/java/com/yahoo/vespa/model/container/xml/ContainerModelBuilder.java