Hadoop Configuration Reference
Apache Hadoop runs on the EC2 instances launched in a cluster. Amazon EMR defines a default configuration for Hadoop, depending on the Amazon Machine Image (AMI) that you specify when you launch the cluster. For more information about the supported AMI versions, see Choose an Amazon Machine Image (AMI).
Although Amazon EMR makes an effort to provide optimal configuration settings for each instance type for the broadest range of use cases, it is possible that you may need to manually adjust these settings for the needs of your application.
The following sections describe the various configuration settings and mechanisms available in Amazon EMR.