You can now launch an EMR cluster with three master nodes and support high availability for HBase clusters on EMR. This is in addition to the support for high availability mode for YARN Resource Manager, HDFS Name Node, Spark, Hive, and Ganglia. Amazon EMR automatically fails over to a standby master node if the primary master node fails or if critical processes such as Resource Manager or Name Node crash. Since the master node is no longer a potential single point of failure with this feature, you can run your long-lived EMR clusters without interruption. In the event of a failover, Amazon EMR automatically replaces the failed master node with a new master node with the same configuration and boot-strap actions.
Please visit Plan and Configure Master nodes to learn more about this feature.
You can stay up to date on EMR releases by subscribing to the feed for EMR release notes. Use the RSS at the top of the EMR Release Guide to link the feed URL directly to your favorite feed reader.
from Recent Announcements https://aws.amazon.com/about-aws/whats-new/2019/05/amazon-emr-now-supports-multiple-master-nodes-to-enable-high-availability-for-hbase-clusters/