Adding a Role Instance

After creating services, you can add role instances to the services. For example, after initial installation in which you created the HDFS service, you can add a DataNode role instance to a host where one was not previously running. Upon upgrading a cluster to a new version of CDH you might want to create a role instance for a role added in the new version. For example, in CDH 5 Impala has the Impala Llama ApplicationMaster Daemon role, which must be added after you upgrade a CDH 4 cluster to CDH 5.

1. Select the service instance for which you want to add a role instance. For example, if you want to add a DataNode role instance, go to the HDFS service.
2. Click the Instances tab.
3. Click the Add button.
4. Customize the assignment of role instances to hosts. The wizard evaluates the hardware configurations of the hosts to determine the best hosts for each role. The wizard assigns all worker roles to the same set of hosts to which the HDFS DataNode role is assigned. These assignments are typically acceptable, but you can reassign services to hosts of your choosing, if desired.

   Click a field below a role to display a dialog containing a pageable list of hosts. If you click a field containing multiple hosts, you can also select All Hosts to assign the role to all hosts or Custom to display the pageable hosts dialog.

   The following shortcuts for specifying host names are supported:

   • Range of hostnames (without the domain portion)

     Range Definition	Matching Hosts
     10.1.1.[1-4]	10.1.1.1, 10.1.1.2, 10.1.1.3, 10.1.1.4
     host[1-3].company.com	host1.company.com, host2.company.com, host3.company.com
     host[07-10].company.com	host07.company.com, host08.company.com, host09.company.com, host10.company.com

   • IP addresses
   • Rack name

   Click the View By Host button for an overview of the role assignment by host ranges.

5. In the Review Changes page review the configuration changes to be applied. Confirm the settings entered for file system paths. The file paths required vary based on the services to be installed. For example, you might confirm the NameNode Data Directory and the DataNode Data Directory for HDFS. Click Continue. The wizard finishes by performing any actions necessary to prepare the cluster for the new role instances. For example, new DataNodes are added to the NameNode dfs_hosts_allow.txt file. The new role instance is configured with the default role group for its role type, even if there are multiple role groups for the role type. If you want to use a different role group, you can go to the Role Groups page under the Configuration tab for the service, and move the role instance to a different role group. See Role Groups for more information. The new role instances are not started automatically.

Starting, Stopping, and Restarting Role Instances

1. Click the service instance that contains the role instance you want to start, stop, or restart.
2. Click the Instances tab.
3. Check the checkboxes next to the role instances to start, stop, or restart (such as a DataNode instance).
4. Select Actions for Selected > Start, Stop, or Restart, and then click Start, Stop, or Restart again to start the process. When you see a Finished status, the process has finished.

Decommissioning Role Instances

If necessary, you can safely remove a role instance such as a DataNode from a cluster while it is running by decommissioning the role instance. When you decommission a role instance, Cloudera Manager performs a procedure for you to safely retire the host on a schedule to avoid data loss. Role decommissioning applies to HDFS DataNodes, MapReduce TaskTrackers, YARN NodeManagers, and HBase RegionServers.

  Note: A role will be decommissioned if its host is decommissioned. In that case, the role will appear as decommissioned on the role instances page for the service. You can recommission the role from this page but the host will need to be recommissioned before any roles that were running on it can be restarted. See Decommissioning a Host for more details.

To decommission role instances:

1. Click the service instance that contains the role instance you want to decommission.
2. Click the Instances tab.
3. Check the checkboxes next to the role instances you want to decommission (such as a DataNode instance).
4. Select Actions for Selected > Decommission, and then click Decommission again to start the process. When you see a Finished status, the decommissioning process has finished.

To recommission role instances:

1. Click the service instance that contains the role instance you want to recommission.
2. Click the Instances tab.
3. Check the checkboxes next to the decommissioned role instances you want to recommission.
4. Select Actions for Selected > Recommission, and then click Recommission again to start the process. When you see a Finished status, the recommissioning process has finished.

If the host for this role instance is currently decommissioned, you will not be able to start this role until the host has been recommissioned.

Deleting Role Instances

1. Click the service instance that contains the role instance you want to delete. For example, if you want to delete a DataNode role instance, click an HDFS service instance.
2. Click the Instances tab.
3. Check the checkboxes next to the role instances you want to delete.
4. If the role instance is running, stop it.
5. Select Actions for Selected > Delete. Click Delete again to confirm the deletion.

  Note: Deleting a role instance does not clean up the associated client configurations that have been deployed in the cluster.