If you are upgrading a cluster that is part of a production
system, be sure to plan ahead. As with any operational work, be sure to reserve
a maintenance window with enough extra time allotted in case of complications.
The Hadoop upgrade process is well understood, but it is best to be cautious.
For production clusters, Cloudera recommends allocating up to a full day
maintenance window to perform the upgrade, depending on the number of hosts, the
amount of experience you have with Hadoop and Linux, and the particular hardware
you are using.
The instructions in this section assume you are upgrading a
multi-node cluster. If you are running a pseudo-distributed (single-machine)
cluster, Cloudera recommends that you copy your data off the cluster, remove the old
CDH release, install Hadoop from CDH 5, and then restore your data.
If you have a multi-node cluster running an earlier version of CDH 5,
use the instructions in one of the following sections to upgrade your cluster to the
latest version: