Dba.getCluster: This function is not available through a session to a standalone instance (RuntimeError)

I am using mysql innodb cluster. Connect to my instance use \c root@localhost:3306. The error message pops out when I issue var cluster = dba.getCluster('testCluster'). I've already created the cluster in last session. But when I reconnect it does not work anymore. The only thing I changed is hostname from localhost to db005 and restart mysql server. Don't even know if it has something to do with my problem. Anybody has idea what happened? Did some searches on google. Seems this is the only resource from mysql forum. But still not able to solve my problem. https://forums.mysql.com/read.php?177,653826,657465#msg-657465 Thx!