We are excited to announce that high-availability EMR on EC2 clusters are now also available with instance fleets configuration. Your high-availability instance fleet EMR cluster will have three on-demand primary nodes and support Hadoop applications like YARN Resource Manager, HDFS Name Node, and Spark. In the event a primary node fails or critical processes like Yarn Resource Manager and NameNode crash, EMR fails over to one of the remaining primary nodes in the cluster.
Source:: Amazon AWS