The following link provides an extensive guide on setting up a multi-node cluser with Hortonworks HDP2 on EC2.
Multi-node cluster installation guide
Though setting up single-node cluster from this guide is quite obvious, I'm documenting here those few so called obvious deviations.
The operating system I choose to install is 64-bit RHEL-6.5_GA-x86_64-7-Hourly2 (ami-8d756fe4) and the instance type as m3.large
and proceeding with the guide as is...
For configuring the password-less SSH login for user ec2-user
$ ssh-keygen -t rsa -P ""
$ cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
Once done this, skip the steps to create other nodes. Since we are going to use only single-node.
Proceed to download ambari.repo, install and start it as shown in the guide. Then launch the browser for ambari's cluster install wizard...
For the Target Hosts specify the same node's private DNS address (single line only).
In the same page, for configuring private key choose .pem file, fill user name as ec2-user.
Continue further and finish the steps as mentioned in the guide... And you are done...
Hope this helps.