Usage:
Create a variables file using ec2_vars/sample.yml as a template.
E.g.
cp ec2_vars/sample.yml ec2_vars/webservers.yml
vi ec2_vars/webservers.yml
After setting all variables, run it:
ansible-playbook -vv -i localhost, -e "type=webservers" provision-ec2.yml
More info: http://allandenot.com/devops/2015/01/31/provisioning-ec2-hosts-with-ansible.html