Rolling upgrade with HA
In the previous few recipes, we enabled high availability using different methods. In this section, we will look at how we can upgrade from one version of Hadoop to another.
The support for rolling upgrades became quite stable in Hadoop 2.4.1 and the clusters can be upgraded without a downtime. HA must be in place if there is a requirement for no downtime in the cluster. In HA, there are Namenodes, Datanodes, ZooKeeper, and Journal nodes. ZooKeeper and Journal nodes are generally stable and do not need an upgrade.
Getting ready
To complete this recipe, the user must have a running cluster with HA set up, as discussed previously. Download the latest stable Hadoop release and untar the package and update the sym-links to point to the newer versions. Refer to the Hadoop installation recipe for details on how the initial setup has been done. Secondly, make sure that the recipes before this have been completed or at least understood.
How to do it...
Connect to the Namenodes...
