You can roll back an upgrade from CDH 4 to CDH 5. The rollback restores your CDH cluster to the state it was in before the upgrade, including Kerberos and TLS/SSL configurations. Any data created after the upgrade is lost.

In a typical upgrade, you first upgrade Cloudera Manager from version 4.x to version 5.x, and then you use the upgraded version of Cloudera Manager 5 to upgrade CDH 4 to CDH 5. (See Upgrading CDH and Managed Services Using Cloudera Manager.) If you want to roll back this upgrade, follow these steps to roll back your cluster to its state prior to the upgrade.

  Important: Follow all of the steps in the order presented in this topic. Cloudera recommends that you read through the backup and rollback steps before starting the backup process. You may want to create a detailed plan to help you anticipate potential problems.

Limitations

The rollback procedure has the following limitations:

• If you have finalized the HDFS upgrade, you cannot roll back your cluster.
• Configuration changes, including the addition of new services or roles after the upgrade, are not retained after rolling back Cloudera Manager.
• Cloudera recommends that you not make configuration changes or add new services and roles until you have finalized the HDFS upgrade and no longer require the option to roll back your upgrade.
• If your cluster is configured to use HBase replication, data written to HBase after the upgrade might not be replicated to peers when you start your rollback. This topic does not describe how to determine which, if any, peers have the replicated data and how to roll back that data. For more information about HBase replication, see HBase Replication.

  Note:

• Hadoop version 2.0, which is included with CDH 4, does not support HDFS rollback for clusters on which high availability is enabled for HDFS. If your CDH 4 cluster has high availability enabled for HDFS, you can temporarily reconfigure your cluster without high availability before proceeding with the rollback. After the rollback, you can re-enable high availability for HDFS. Procedures for these reconfigurations are provided in the rollback procedures.
• Because of an HDFS bug, rollback fails on DataNodes because the DataNode storageID format changed between the Hadoop versions used in CDH 4 and CDH 5. The workaround is described in the rollback procedures.