Managing Roles
When Cloudera Manager configures a service, it configures host machines in your cluster with one or more functions (called roles in Cloudera Manager) that are required for that service. The role determines which Hadoop daemons run on a given host. For example, when Cloudera Manager configures an HDFS service instance it configures one host to run the NameNode role, another host to run as the Secondary NameNode role, another host to run the Balancer role, and some or all of the remaining hosts as to run DataNode roles.
The configuration settings for a particular role type are organized in role groups. A role group includes a set of configuration properties for a specific role type, as well as a list of role instances associated with that role group. Cloudera Manager automatically creates a default role group for each role type. For role types that allow multiple instances on multiple nodes, such as DataNodes, TaskTrackers, RegionServers (and many others), you can create multiple role groups to allow one set of role instances to use different configuration settings than another set of instances of the same role type.