You can now create Amazon EMR clusters in private subnets in your Amazon Virtual Private Cloud (VPC). Previously,Amazon EMR only supported creating clusters in public subnets, which required an attached Internet gateway. With Amazon EMR release 4.2.0 and later, or you can now also launch your clusters in a private subnet with no public IP addresses or attached Internet gateway. You can create an endpoint for Amazon S3 in your VPC to give your Amazon EMR cluster direct access to data in Amazon S3,and optionally create a Network Address Translation (NAT) instance for your cluster to interact with other AWS services that attain not currently support endpoints in VPC.
Source: amazon.com