To deploy kubespray on AWS uncomment the cloud_provider option in group_vars/all.yml and set it to 'aws'.
Prior to creating your instances, you must ensure that you have created IAM roles and policies for both "kubernetes-master" and "kubernetes-node". You can find the IAM policies here. See the IAM Documentation if guidance is needed on how to set these up. When you bring your instances online, associate them with the respective IAM role. Nodes that are only to be used for Etcd do not need a role.
The next step is to make sure the hostnames in your inventory file are identical to your internal hostnames in AWS. This may look something like ip-111-222-333-444.us-west-2.compute.internal. You can then specify how Ansible connects to these instances with ansible_ssh_host and ansible_ssh_user.
You can now create your cluster!