When we are adding the mounttable entry, the router sever is terminated.
Some error messages show in log, as follow:
2018-08-20 14:18:32,404 ERROR org.apache.hadoop.hdfs.server.federation.store.driver.impl.StateStoreZooKeeperImpl: Cannot get data for 0SLASH0testzk: null.
The reason is that router server have created the znode but not to set data before being terminated. But the method zkManager.getStringData(path, stat) will throw NPE if the path has null value in the StateStoreZooKeeperImpl, leading to fail in adding the same mounttable entry and deleting the existing znode.