Major Description
As the title describes the problem: if the include host list contains host name, after restarting namenodes, the datanodes registrant is denied by namenodes. This is because after namenode is restarted, the still alive data node will try to register itself with the namenode and it identifies itself with its IP address. However, namenode only allows all the hosts in its hosts list to registrant and all of them are hostnames. So namenode would deny the datanode registration.