4.1. Perform Rolling Upgrade

Ambari will check that your cluster meets the Rolling Upgrade Prerequisites. A dialog will be presented with the results:

If any prerequisites are not met but are required, the result will be shown with an error. You will not be allowed to proceed with the upgrade. Make the appropriate corrections and return to Perform Upgrade again.
If any prerequisites are not met but are optional, the result will be shown with a warning. You will be allowed to Proceed with the upgrade.
A list of configuration changes (if any) will be displayed.

Once the prerequisite checks are complete, the upgrade will start. The time it takes to perform the upgrade dependents on many factors. As part of the upgrade process, each component in the cluster is restarted in a serial fashion as such, the stop/start time is a big contributor to the overall time.

The upgrade process involves a set of stages. This table lists the high-level stages and if the process requires any action by you during normal operation.

	Note
	If any stage fails, the upgrade will halt and prompt for action.

Stage	Description	Action Required
Prepare Backups	This is a confirmation step used to confirm that you have taken proper backups before proceeding.	You must acknowledge the prompt for database backups.
ZooKeeper	All ZooKeeper servers are upgraded and restarted.	None
Ranger	Ranger Admin and UserSync servers are upgraded and restarted.	None. If Ranger Admin does not function after the upgrade completes, run the upgrade scripts manually, then Retry Upgrading Ranger, as described here.
Core Masters	This stage upgrades the master components of core services. This includes JournalNodes & NameNodes (HDFS), HistoryServer (MapReduce2), ResourceManager & ATS (YARN) and HBase Masters (HBase).	None
All Service Checks	All Service Checks are performed against the cluster.	If any service check fails, you will be prompted to Ignore and Continue, Downgrade or Retry. If you selected the "Skip all Service Check failures" option, you will only be prompted at the completion of all of the Service Checks.
Core Slaves	This stage upgrades the slave components of core services. This includes DataNodes (HDFS), RegionServers (HBase) and NodeManagers (YARN). This is down in two batches: 20% of the slaves first, then the remaining slaves.	After the first 20% batch is complete, you will be prompted to Verify the cluster is operating correctly.
All Service Checks	All Service Checks are performed against the cluster.	If any service check fails, you will be prompted to Ignore and Continue, Downgrade or Retry. If you selected the “Skip all Service Check failures” option, you will only be prompted at the completion of all of the Service Checks.
Hive	This stage upgrades the Hive Metastore, HiveServer2 and WebHCat components and the Hive clients.	Ambari will switch the HiveServer2 port from 10000 to 10010 (or, 10011 if using HTTP transport mode). You will be prompted to confirm prior to the switch.
Spark	The Spark Job History Server and clients are upgraded.	None
Oozie	The Oozie Server and clients are upgraded.	None
Falcon	The Falcon Server and clients are upgraded.	None
Client Components	All remaining clients are upgraded.	None
All Service Checks	All Service Checks are performed against the cluster.	If any service check fails, you will be prompted to Ignore and Continue, Downgrade or Retry. If you selected the “Skip all Service Check failures” option, you will only be prompted at the completion of all of the Service Checks.
Kafka	The Kafka Brokers are upgraded.	None
Knox	The Knox Gateways are upgraded.	None
Storm	The Nimbus, REST API, DRPC Server and UI Server components are upgraded, along with the Supervisors.	None
Slider	The Slider clients are upgraded.	None
Flume	The Flume agents are upgrade.	None
Finalize Upgrade Pre-Check	Checks if any hosts were not upgraded, either because the host was in Maintenance Mode, or one or more components on the host failed to upgrade (and were skipped).	Click on the list that displays "# hosts" for details on the hosts (and their components) that are not upgraded. You can Pause Upgrade, delete the hosts and return to finalize.
Finalize	The component upgrades are complete. You are presented the option to Finalize, which when selected, completes the upgrade process + saves the cluster state.	Prompted to Finalize, Finalize Later or Downgrade.

Once the upgrade is complete, you have an option to Finalize the upgrade, to Finalize Later or to Downgrade. Finalizing later gives you a chance to perform more validation on the cluster. Downgrade moves the cluster version back to the previous version (basically: the reverse of the upgrade process stages). Once finalized, you cannot downgrade back to the previous version.

	Note
	If you choose to finalize later, both versions will be listed on the Stack and Versions tab with the starting version displaying as Current. It is not until you finalize that Ambari makes the target version the current version. Also, until you finalize, you will not be able to perform operational changes to the cluster (such as move components, change configurations, etc).

Click Finalize and the upgrade process is complete.

​4.1. Perform Rolling Upgrade