最新のAmazon Linux AMIのIDを取得する ref: http://qiita.com/imaifactory/items/35acd4b8b9f96f7d712b

latest_amazonlinux_ami.rb

#!/usr/bin/env ruby
require 'aws-sdk-core'

ec2 = Aws::EC2::Client.new(region:'ap-northeast-1')
images = ec2.describe_images(
    owners: ['amazon'],
    filters: [
        {
            name:"architecture",
            values:["x86_64"]
        },
        {
            name:"hypervisor",
            values:["xen"]
        }
    ]
)

latest_ami = images[:images].find_all{|image|
    image[:description]
}.find_all{|image|
        image[:description].match(/Amazon Linux/)
}.find_all{|image|
        image[:description].match(/EBS/)
}.find_all{|image|
        image[:description].match(/HVM/)
}.sort_by{|image|
    image[:creation_date]
}.reverse.first

puts latest_ami[:image_id]