private Reader retrieveConfigDefReader(String def) {
        try {
            return zkApplication.getNamedReader("configdefinition", Path.fromString(DEFCONFIGS_ZK_SUBPATH).append(def));
        } catch (IllegalArgumentException e) {
            throw new IllegalArgumentException("Could not retrieve config definition " + def, e);
        }
    }
Reads allocated hosts at the given node.

@return the allocated hosts at this node or empty if there is no data at this path
configserver/src/main/java/com/yahoo/vespa/config/server/zookeeper/ZKApplicationPackage.java