This is the documentation for Cloudera Manager 4.8.3.
Documentation for other versions is available at Cloudera Documentation.

Decommissioning a Host

Decommissioning a Host

Decommissioning a host lets you decommission all roles on a single host without having to go to each service and decommission the roles individually. Once all roles on the host have been decommissioned and stopped, the host can be removed from service.

Decommissioning applies to only to HDFS DataNodes, MapReduce TaskTrackers, YARN NodeManagers, and HBase RegionServers. If the host you select has other roles running on it, those roles will simply be stopped.

Host decommissioning supports decommissioning multiple hosts in parallel.

To decommission one or more hosts:

  1. Click the Hosts tab.
  2. Select the host(s) you want to decommission.
  3. From the Actions for Selected menu, click Decommission.

A confirmation pop-up informs you of the roles that will be decommissioned or stopped on the nodes you have selected. To proceed with the decommissioning, click Confirm.

A Command Details window appears that will show each stop or decommission command as it is run, service by service. You can click one of the decommission links to see the subcommands that are run for decommissioning a given role. Depending on the role, the steps may include adding the node to an "exclusions list" and refreshing the NameNode, JobTracker, or NodeManager, stopping the Balancer (if it is running), and moving data blocks or regions. Roles that do not have specific decommission actions are just stopped.

While decommissioning is in progress, the host is marked Decommissioning in the list under the Hosts tab. Once all roles have been decommissioned or stopped, the host is marked Decommissioned.

Roles on a decommissioned host cannot be restarted until the host is recommissioned.

Recommissioning a Host

Only hosts that are decommissioned using Cloudera Manager can be recommissioned.

To recommission one or more hosts:

  1. Click the Hosts tab.
  2. Select the host(s) you want to recommission.
  3. From the Actions for Selected menu, click recommission.

This will recommission the host (i.e. remove it from the exclusion lists and run the appropriate refresh) so that the roles that reside on it can be restarted. The Decommissioned indicator is removed from the host. It also removes the Decommissioned indicator from the roles that reside on the host. However, the roles themselves are NOT restarted by the recommission command.

You can restart all the roles on a recommissioned host in a single command from the Hosts page:

  1. Select the host(s) on which you want to start the decommissioned roles.
  2. From the Actions for Selected menu, click Start All Roles.

This will start all the roles on the selected host.