Adding a Role Instance

Required Role:

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 role, which must be added after you upgrade a CDH 4 cluster to CDH 5.

1. Go to the service for which you want to add a role instance. For example, to add a DataNode role instance, go to the HDFS service.
2. Click the Instances tab.
3. Click the Add Role Instances 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 role instances 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 hostname patterns 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 hostname 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, follow the instructions in Managing Role Groups for moving role instances to a different role group. The new role instances are not started automatically.

Starting, Stopping, and Restarting Role Instances

Required Role:

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

1. Go to the service that contains the role instances 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

Required Role:

You can remove a role instance such as a DataNode from a cluster while the cluster is running by decommissioning the role instance. When you decommission a role instance, Cloudera Manager performs a procedure so that you can safely retire a host without losing data. Role decommissioning applies to HDFS DataNode, MapReduce TaskTracker, YARN NodeManager, and HBase RegionServer roles.

A role will be decommissioned if its host is decommissioned. See Decommissioning and Recommissioning Hosts for more details.

  Note: You cannot decommission a DataNode or a host with a DataNode if the number of DataNodes equals the replication factor (which is by default 3) of any file stored in HDFS. For example, if the replication factor of any file is three, and you have three DataNodes, you cannot decommission a DataNode or a host with a DataNode.

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 to decommission.
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.

While decommissioning is in progress, the role instance displays the icon. If one role instance of a service is decommissioned, the DECOMMISSIONED facet displays in the Filters on the Instances page and the icon displays on the role instance's page.

Recommissioning 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 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.

Deleting Role Instances

Required Role:

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, select Actions for Selected > Stop and click Stop to confirm the action.
5. Select Actions for Selected > Delete. Click Delete to confirm the deletion.

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