Deleting Hosts

You can stop Cloudera Manager from managing a host and the Hadoop daemons on the host.

First, make sure there are no roles running on the Host; you can decommission the host to ensure all roles are stopped.

Second, you must stop the Cloudera Manager Agent from running on the host; if you don't stop the Agent, it will send heartbeats to the Cloudera Manager Server and show up again in the list of hosts.

To delete a host:

1. Decommission the host to ensure all roles on the host have been stopped. For instruction, see Decommissioning a Host.
2. Stop the Agent on the host. For instructions, see Stopping and Restarting Cloudera Manager Agents.
3. In the Cloudera Manager Admin Console, click the Hosts tab.
4. Select the host in the Hosts tab.
5. From the Actions for Selected menu, select Delete.

Reference : http://www.cloudera.com/content/cloudera-content/cloudera-docs/CM4Free/4.5.1/Cloudera-Manager-Free-Edition-User-Guide/cmfeug_topic_6_7.html

Note : Atleast 1 hbase master should run while decommission  So, the region data will be swap to another region server. So, make sure hbase and other services running. Cloudera will take care of adding into excluding list safely

Also make sure the agents on cloudera machines were stopped else the host will be displayed automatically on cloudera