aws_creds.rb is used to fill AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY variables from AWS_CREDENTIAL_FILE

ec2.rb is a bunch of helpers to use them in irb

EC2Conn automatically sets up connection on first use (using credentials from aws_creds) so you need not invoke it by hand. EC2Conn.groups prints all security groups which include at least one instance. EC2Conn.each_group runs the specified block for each instance of specified group (or groups) All other method calls are passed to RightAws::Ec2 object.