Cloudera Docs

Decommissioning Hosts

Cloudera Manager manages the host decommission and recommission process and allows you the option to specify whether to replicate the data to other DataNodes, and whether or not to suppress alerts.

Decommissioning a host decommissions and stops all roles on the host without requiring you to individually decommission the roles on each service. Decommissioning applies only to the following service roles, other roles running on the host are stopped:
  • HDFS DataNode
  • MapReduce TaskTracker
  • YARN NodeManager
  • HBase RegionServer
  • Kafka Broker

    Decommissioning only applies to the Kafka Broker role if Cruise Control is installed on the cluster. When a Kafka Broker role is decommissioned, Cruise Control moves the data and partitions from the selected broker role to other broker roles in the cluster. For more information about decommissioning Kafka brokers, see Scaling Kafka brokers.

Hosts with DataNodes and DataNode roles themselves can only be decommissioned if the resulting action leaves enough DataNodes commissioned to maintain the configured HDFS replication factor (by default 3). If you attempt to decommission a DataNode or a host with a DataNode in such situations, the decommission process will not complete and must be aborted.

Minimum Required Role: Limited Operator (also provided by Operator, Configurator, Cluster Administrator, Limited Cluster Administrator , or Full Administrator).

To decommission one or more hosts:
  1. If the host has a DataNode, and you are planning to replicate data to other hosts (for longer term maintenance operations or to permanently decommission or repurpose the host), perform the steps in Tuning HDFS Prior to Decommissioning DataNodes.
  2. In Cloudera Manager, select the cluster where you want to decommission hosts.
  3. In the left menu, click Hosts > All Hosts.
  4. Select the hosts that you want to decommission.
  5. Select Actions for Selected > Begin Maintenance (Suppress Alerts/Decommission.
    (If you are logged in as a user with the Limited Operator or Operator role, the menu item is labeled Decommission Host(s) and you will not see the option to suppress alerts.)
    The Begin Maintenance (Suppress Alerts/Decommission) dialog box opens. The role instances running on the hosts display at the top.
  6. To decommission the hosts and suppress alerts, select Decommission Host(s). When you select this option for hosts running a DataNode role, choose one of the following (if the host is not running a DataNode role, you will only see the Decommission Host(s) option:):
    • Decommission DataNodes

      This option re-replicates data to other DataNodes in the cluster according to the configured replication factor. Depending on the amount of data and other factors, this can take a significant amount of time and uses a great deal of network bandwidth. This option is appropriate when replacing disks, repurposing hosts for non-HDFS use, or permanently retiring hardware.

    • Take DataNode Offline
      This option does not re-replicate HDFS data to other DataNodes until the amount of time you specify has passed, making it less disruptive to active workloads. After this time has passed, the DataNode is automatically recommissioned, but the DataNode role is not started. This option is appropriate for short-term maintenance tasks such not involving disks, such as rebooting, CPU/RAM upgrades, or switching network cables.
  7. Click Begin Maintenance.
    The Host Decommission Command dialog box opens and displays the progress of the command.
Perform the necessary maintenance on the hosts.