Hadoop

Commission/decommission a node

When you want to remove the node from the cluster, you shouldn’t just delete the cloudera agents, services installed as it will impact the whole cluster. You should go for decommission first.

Decommissioning a host decommissions and stops all roles on the host without requiring you to individually decommission the roles on each service.

After all the roles on the host have been decommissioned and stopped, the host can be removed from service. You can decommission multiple hosts in parallel.

To decommission a host, go to CM – Hosts – select the checkbox of the hosts – click Actions for Selected

Select Hosts decommission – Confirm

Once the host is decommissioned, the “Commission state” of the host will change to “Decommissioned”.

Note:

You cannot decommission a DataNode or a host with a DataNode if the number of DataNodes equals the replication factor (which by default is three) 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. If you attempt to decommission a DataNode or a host with a DataNode in such situations, the DataNode will be decommissioned, but the decommission process will not complete.

Either you have to add one more datanode to the cluster, run the balancer to distribute the blocks or you have to change the replication factor of all blocks in the node to less than 3, then proceed to decommission the host.

Recommission

Recommission is applicable only for hosts decommissioned using Cloudera Manager.

Go to CM – Hosts – select decommissioned hosts – Actions for selected – Hosts Recommission – confirm

Thus we covered how to Commission/decommission a node.

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