Amazon EMR - RDS DB Security Group

Log in to your AWS RDS console. Select Security Groups on the left sidebar.

Select your DB Security Group and click on the Edit button.

Add the following:

1.) EMR master

Connection Type = EC2 Security Group
EC2 Security Group = ElasticMapReduce-master

2.) EMR slave

Connection Type = EC2 Security Group
EC2 Security Group = ElasticMapReduce-slave