An Amazon EMR cluster is defined using the AWS::EMR::Cluster resource. This cluster consists of Amazon EC2 servers that handle and analyse massive volumes of data using open source big data frameworks and apps. The Amazon EMR Management Guide provides more information.
As part of the AWS::EMR::Cluster resource, Amazon EMR now allows you to launch task instance groups and fleets. Use the TaskInstanceGroups and TaskInstanceFleets subproperties of the JobFlowInstancesConfig property type to do this. When compared to using the AWS::EMR::InstanceGroupConfig and AWS::EMR::InstanceFleetConfig resources to specify task nodes, using these subproperties reduces provisioning time. For more information on how to utilise these subproperties, see the examples at the bottom of the page.