A role group is a set of configuration properties for a role type, as well as a list of role instances associated with that group. Cloudera Manager automatically creates a default role group named Role Type Default Group for each role type.Each role instance can be associated with only a single role group.
Role groups provide two types of properties: those that affect the configuration of the service itself and those that affect monitoring of the service, if applicable (the Monitoring subcategory). Not all services have monitoring properties.
When you run the installation or upgrade wizard, Cloudera Manager configures the default role groups it adds, and adds any other required role groups for a given role type. For example, a DataNode role on the same host as the NameNode might require a different configuration than DataNode roles running on other hosts. Cloudera Manager creates a separate role group for the DataNode role running on the NameNode host and uses the default configuration for DataNode roles running on other hosts.
You can modify the settings of the default role group, or you can create new role groups and associate role instances to whichever role group is most appropriate. This simplifies the management of role configurations when one group of role instances may require different settings than another group of instances of the same role type—for example, due to differences in the hardware the roles run on. You modify the configuration for any of the service's role groups through the Configuration tab for the service. You can also override the settings inherited from a role group for a role instance.
If there are multiple role groups for a role type, you can move role instances from one group to another. When you move a role instance to a different group, it inherits the configuration settings for its new group.