Amazon EMR now supports launching clusters with custom Amazon Linux AMIs

You can now create Amazon EMR clusters with custom Amazon Machine Images (AMI) running Amazon Linux. This enables you to preload additional software on your AMI and use AMIs that you customize and control. You can also encrypt the Amazon EBS root volume of your AMIs with AWS Key Management Service (KMS) keys. Additionally, you can now adjust the Amazon EBS root volume size for instances in your Amazon EMR cluster. Previously, this was fixed at 10 GiB.  
Quelle: aws.amazon.com