The Migrate Roles wizard allows you to move roles of a highly available HDFS service from one host to another. You can use it to move NameNode, JournalNode, and Failover Controller roles.

Requirements and Limitations

• Nameservice federation (multiple namespaces) is

  not supported

  .

• This procedure requires cluster downtime. The services discussed in this list must be running for the migration to complete.

• The configuration of HDFS and services that depend on it must be valid.

• The source and destination hosts must be commissioned and healthy.

• The NameNode must be highly available using quorum-based storage.

• HDFS automatic failover must be enabled, and the cluster must have a running ZooKeeper service.

• If a Hue service is present in the cluster, its HDFS Web Interface Role property must refer to an HttpFS role, not to a NameNode role.

• A majority of configured JournalNode roles must be running.

• The Failover Controller role that is not located on the source host must be running.

Before You Begin

Do the following before you run the wizard:

• On hosts running active and standby NameNodes, back up the data directories.
• On hosts running JournalNodes, back up the JournalNode edits directory.
• If the source host is not functioning properly, or is not reliably reachable, decommission the host.
• If CDH and HDFS metadata was recently upgraded, and the metadata upgrade was not finalized, finalize the metadata upgrade.

Running the Migrate Roles Wizard

1. If the host to which you want to move the NameNode is not in the cluster, follow the instructions in Adding a Host to the Cluster to add the host.

2. Go to the HDFS service.

3. Click the Instances tab.

4. Click the Migrate Roles button.

5. Click the Source Host text field and specify the host running the roles to migrate. In the Search field optionally enter hostnames to filter the list of hosts and click Search.

   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

   Select the checkboxes next to the desired host. The list of available roles to migrate displays. Clear any roles you do not want to migrate. When migrating a NameNode, the co-located Failover Controller must be migrated as well.

6. Click the Destination Host text field and specify the host to which the roles will be migrated. On destination hosts, indicate whether to delete data in the NameNode data directories and JournalNode edits directory. If you choose not to delete data and such role data exists, the Migrate Roles command will not complete successfully.

7. Acknowledge that the migration process incurs service downtime by selecting the Yes, I am ready to restart the cluster now checkbox.

8. Click Continue. The Command Progress screen displays listing each step in the migration process.

9. When the migration completes, click Finish.